Please write a Scheme function in the DrRacket IDE which returns a string containing only the number characters in the given string. For example, if the given string is "12dffggb4@#$%5d", then the return string is "1245". You are required to

1. use a loop or recursion to find the number characters in a character-by-character analysis;
2. provide an explanation as the program comments for the algorithm you are using;
3. call your function using the strings "12dffggb4@#$%5d", "sg6#7 F^T8c fi1 0d(@DK4", and show the return strings.