a)
0 ice cream cost $0 (f(0) = 0 * $0.79 = $0)
1 ice cream cost $0.79 (f(1) = 1 * $0.79 = $0.79)
2 ice creams cost $1.58 (f(2) = 2 * $0.79 = $1.58)
3 ice creams cost $0.79 (f(3) = 3 * $0.79 = $2.37)
b)
so x ice creams cost $.79 x (f(x) = x * $0.79 = $0.79x)
function f(x) = 0.79x
Hope it helps