f(x) means y
for function f y is proportional to x
so for the first one
f(x) = 4x^5
the point (2,80)
f(2) = 4(2)^5
f(2) = 4*32
f(2) = 128
The answer is not the first one
the second
f(x) = 5x^4
f(2) = 5(2)^4
f(2) = 5(16)
f(2) = 80
so the second function is the answer
