Completed Step 1 of arithmetic.php

Added code inside each function to perform the appropriate operation.
Completed Step 2 of arithmetic.php

Added code after functions to call functions and pass real numbers.
Added new line to each function’s echo statement.
Completed Step 4 and 5 of arithmetic.php

Added function that finds the modulus of two numbers. Called the
modulus function and passed real numbers. Verified output of functions.