Write a method that accepts two string input parameters. 'orig' is the original string and 'sub' is the substring to find in the original string. Return the LAST occurance of 'sub' within 'orig' or if 'sub' does not occur in 'orig' return -1. Note that 'sub' will NOT be longer than 'orig' and neither string will be empty. You may only use the following string methods in solving this problem: .length .substring .equals .charAt