AP Computer Science A FRQ CheckDigit

Both the instructions on pages 199-202 and the quick reference guide on page 209 are available at this link: https://apcentral.collegeboard.org/pdf/ap-computer-science-a-course-and-exam-description.pdf?course=ap-computer-science-a

Correct solution and scoring guidelines are available at this link:

https://apcentral.collegeboard.org/pdf/ap-computer-science-a-2019-ced-scoring-guidelines.pdf?course=ap-computer-science-a

The correct answer outputs should be as follows.

Part A
getCheck(283415) -> 6
getCheck(2183) -> 2

Part B
isValid(1592) -> true => valid combo of 159 and its check digit 2
isValid(1593) -> false => not a valid combo of number 159 and check digit 3 because the check digit of 159 is 2.