in C++

Given the following recursive function: string mystery(string s) return i ()r if (toupper s]) 'A' 11 toupper (s 'E Il toupper(s[ 0 ])--T Il toupper(s[ 0 ])-= .0' II toupper(sI ) U') return s.substr(0, 1) mystery(s.substr(1, s.size() 1)) return ""+mystery(s.substr(1, s.size() -1)) Show all the calls to the function and what each one returns to its predecessor. string result = mystery("Omar"); Call # 1. mystery("Omar") returns 2. mystery" 3. mystery 4. mystery 5. mystery("") returns "" to Call #4. Describe what the mystery method accomplishes. to result ") returns ) returns ) returns to Call to Call #2 to Call