MATH QUESTION Please help

Which of the following best describes the graph below? a. it is a function, but it is not one-to-one. b. it is a one-to-one function. c. it is not a function. d. it is a many-to-one function.

Carson has only $20 bills and $10 bill in her wallet. the total value of the bills is $50. she has 1 more $20 bill than $10 bills. how many each kind of bill does carson have? a. one $20 and two $10 bills b. two $20 bills and one $10 bill c. one $20 bills and three $10 bills d. two $20 bills and two $10 bills

How can i differentiate this equation?