In all calculations firstly do the Parentheses.
Then go for Exponents.
Then go for Multiplication and Division (from left hand side to the right hand side)
And then finally do the Addition and Substraction (also from left to the right)
You can remember it as PEMDAS: Pudgy Elves May Demand A Snack
In this case just follow the calculations from left to right as it's just about adding and substracting, so it'll look like:
A + B + 2A - 3B = 3A - 2B
