1 5 6 7

You may use each of the numbers 1, 5, 6 and 7 only once. You may use each of the operations +, -, x and / as many or as little times as you like. Parentheses are fare game too. You may not use the numbers to make more than one-digit numbers. (e.g. Using 1 and 5 to make 15) The goal is to make an expression equal to 21.