The definition of an "excellentMashUp" of two positive integers is the product of the sums of each of their digits. So the "semiproduct" of 21 and 71 is 24 because 2+1=3 and 7+1=8, then 3*8=24. Decompose out a separate digitSum(int n) method that finds the sum of the digits of a positive integer. You MUST use recursion in the digitSum method in order to earn credit for this problem.