diff --git a/src/040-deriving-types-from-values/128-classes-and-enums-cross-value-and-type-world.problem.ts b/src/040-deriving-types-from-values/128-classes-and-enums-cross-value-and-type-world.problem.ts
deleted file mode 100644
index e69de29..0000000
diff --git a/src/040-deriving-types-from-values/128-classes-and-enums-cross-value-and-type-world.solution.ts b/src/040-deriving-types-from-values/128-classes-and-enums-cross-value-and-type-world.solution.ts
deleted file mode 100644
index e69de29..0000000
diff --git a/src/040-deriving-types-from-values/128-classes-cross-value-and-type-world.problem.ts b/src/040-deriving-types-from-values/128-classes-cross-value-and-type-world.problem.ts
new file mode 100644
index 0000000..2a6d592
--- /dev/null
+++ b/src/040-deriving-types-from-values/128-classes-cross-value-and-type-world.problem.ts
@@ -0,0 +1,30 @@
+import { describe, expect, it } from "vitest";
+
+class CanvasNode {
+  x = 0;
+  y = 0;
+
+  move(x: number, y: number) {
+    this.x = x;
+    this.y = y;
+  }
+}
+
+const positionFromCanvasNode = (node) => {
+  return {
+    x: node.x,
+    y: node.y,
+  };
+};
+
+describe("positionFromCanvasNode", () => {
+  it("Should return the position of the node", () => {
+    const canvasNode = new CanvasNode();
+
+    expect(positionFromCanvasNode(canvasNode)).toEqual({ x: 0, y: 0 });
+
+    canvasNode.move(10, 20);
+
+    expect(positionFromCanvasNode(canvasNode)).toEqual({ x: 10, y: 20 });
+  });
+});
diff --git a/src/040-deriving-types-from-values/128-classes-cross-value-and-type-world.solution.ts b/src/040-deriving-types-from-values/128-classes-cross-value-and-type-world.solution.ts
new file mode 100644
index 0000000..cb9a889
--- /dev/null
+++ b/src/040-deriving-types-from-values/128-classes-cross-value-and-type-world.solution.ts
@@ -0,0 +1,31 @@
+import { describe, expect, it } from "vitest";
+
+class CanvasNode {
+  x = 0;
+  y = 0;
+
+  move(x: number, y: number) {
+    this.x = x;
+    this.y = y;
+  }
+}
+
+// Look at typeof CanvasNode
+const positionFromCanvasNode = (node: CanvasNode) => {
+  return {
+    x: node.x,
+    y: node.y,
+  };
+};
+
+describe("positionFromCanvasNode", () => {
+  it("Should return the position of the node", () => {
+    const canvasNode = new CanvasNode();
+
+    expect(positionFromCanvasNode(canvasNode)).toEqual({ x: 0, y: 0 });
+
+    canvasNode.move(10, 20);
+
+    expect(positionFromCanvasNode(canvasNode)).toEqual({ x: 10, y: 20 });
+  });
+});
diff --git a/src/040-deriving-types-from-values/129-this-crosses-value-and-type-world.explainer.ts b/src/040-deriving-types-from-values/129-this-crosses-value-and-type-world.explainer.ts
new file mode 100644
index 0000000..4430dba
--- /dev/null
+++ b/src/040-deriving-types-from-values/129-this-crosses-value-and-type-world.explainer.ts
@@ -0,0 +1,19 @@
+class CanvasNode {
+  x: number;
+  y: number;
+
+  constructor(x: number, y: number) {
+    this.x = x;
+    this.y = y;
+  }
+
+  move(x: number, y: number): this {
+    this.x += x;
+    this.y += y;
+    return this;
+  }
+}
+
+const node = new CanvasNode(0, 0).move(10, 20).move(30, 40);
+
+type test = Expect<Equal<typeof node, CanvasNode>>;
diff --git a/src/040-deriving-types-from-values/129-this-crosses-value-and-type-world.problem.ts b/src/040-deriving-types-from-values/129-this-crosses-value-and-type-world.problem.ts
deleted file mode 100644
index e69de29..0000000
diff --git a/src/040-deriving-types-from-values/129-this-crosses-value-and-type-world.solution.ts b/src/040-deriving-types-from-values/129-this-crosses-value-and-type-world.solution.ts
deleted file mode 100644
index e69de29..0000000