need help writing a MIPS program will read in a value (nonnegative integer but as an ASCII string) in base 64and print out the decimal value; you

need help writing a MIPS program will read in a value (nonnegative integer but as an ASCII string) in base 64 and print out the decimal value; you must implement a function (which accepts an address for a string as the parameter, and returns the value) and call the function from the main program.