Given the following four numbers:

1 5 6 7

The goal is to make the number:

21

Using only these elementary arithmetic operations:

( + − × ÷ )

1 5 6 7

The goal is to make the number:

21

Using only these elementary arithmetic operations:

( + − × ÷ )

So, you can put the four numbers in any order, and use parentheses to specify operator precedence. Each number may only be used once and must be used separately (i.e. no sticking numbers together). You do not necessarily need to use all the operators.

What would the resulting equation look like?