Please explain the answer clearly and write the answer neatly.
Problem 7. For each of the functions below, indicate whether the function is onto, one-to-one, neither, or both. If the function is not onto or not one-to-one, give an example showing why.
(a) f1: Z → Z, f1(x) = x^3
(b) f2: Z → Z, f2(x) = |x| + 2
(c) f3: Z x Z → Z, f3(x,y) = (x+1, 2y)
(d) f4: Z+Z+Z → Z, f4(x,y) = 2 + y - 1