Part A: yes it is a function because every input value (x) produces only one output value (y).
Note: It is still a function if different x values produce the same y value, in this case, x=1 and x=-1 produce the same y value 1, but it is NOT a function if y=1 and y=-1 have the same x value x=1.
Part B: when x=30: f(30)=17*30+50=560
if means that the cost of renting the truck for 30 hours is 560 dollars.
