1) Write a function that takes a, b, and c and return a string of the tree values in sorted order. You might want to write a function combine abc that returns a contact ":" b contact ":" contact c. You will use string_of_int function to convert int to string. \( \begin{array}{lll}\text { sort_as_str } 546 ; & 4 & \text { return } \\ \text { "4:5:6" } \\ \text { sort_as_str } 465 ; ; & \text { return } \\ \text { "4:5:6" } & \\ \text { sort_as_str } 456 ; ; & \text { return } \\ \text { "4:5"6" }\end{array} \)