(b) The following C++ function multiplies natural numbers x and y by repeated addition. Derive, and prove correct, the number of "+" operations this method executes. int multiply (int x, int y) ( } if (y > 0) { return x +multiply (x, y-1); { else { } } (c) The following C++ function writes long string of "x"s. Derive, and prove correct, the length of this string, as function of n. return 0; void longString (int n) { if (n > 0) { } longString (n-1); longString (n-1); } else { cout