f(x) = 100 - 3.3x
This function can represent the final letter grade you will have with "x" being the number of questions you get wrong.
If I get 10 questions wrong this means my grade drops to 100-3.3(10) = 67%
If I get 0 questions wrong this means my final grade is: 100 - 3.3(0) = 100%
This also means that the total number of questions on the exam is 30 questions