In a function, for every number for 'x' there is only one 'y'. So, if you have two ordered pairs in a choice that have the same number for 'x', that is not a function.
Remember an ordered pair is written (x, y).
B is not a function as: (x, y) (1, -2) (1, -3) (1, -4) ^ All of the x-coordinates are the same.
E is not a function as: (x, y) (6, -1) (6, -8) ^ Two of the x-coordinates are the same.
Interest accumulates whether he pays or not. If he does not pay, the principal is not reduced, therefore the accumulated amount in 15 months is equal to Future value = 13000(1+0.036/12)^15 =$13597.45 (to the nearest cent)
