The table below shows the fourth roots of different numbers:

number (x) 1 1 81 81
fourth root of the number (y) 1 −1 3 −3

part a: does the table represent y as a function of x? justify your answer. (5 points)

part b: the total cost f(x), in dollars, for renting a truck for x hours is shown below:

f(x) = 25x + 16

what is the value of f(20) and what does f(20) represent? (5 points)