Query about Question 1 from "PrepSwift: Adding Numbers to Multiples" [3617]

https://prepswift.gregmat.com/quizzes/quiz/prepswift-adding-numbers-to-multiples (Question 1)


How to solve this question?

a = b + 5

When b = 1 = odd, a = 6.

When b = 0 = even, a = 5.

When one is even, the other is odd and vice versa