In mathematics in order to avoid ambiguity of calculation as to which operation should be performed first we have to use a standard rule in precedence of operations:

The order of operations is as follows:

1. Evaluate the parenthesis, if there are any, and if they require evaluation. If more than two parenthesis are there begin from the inner most one.
2. Evaluate the powers or the exponents.
3. Multiply or divide-it doesn’t matter. Proceed from left to right.
4. Add or subtract. Proceed from left to right.