26. For appropriate sets A and B, determine the range of a function f : A → B that assigns (a) to each integer the sum of that integer and its negative. (b) to each pair of integers the sum of twice of the first integer and three times the second integer. (c) to each real number the cube root of that number. (d) to each rational number two times that number. (e) to each positive 2-digit integer the first digit of that integer.