He received 30 dollars in commission
You will need to follow order of operations, which states that operations must be completed in the following order: parentheses, exponents, multiplication and division, and then addition and subtraction.
In this case, there are no parentheses and no exponents, so we will start with the multiplication and division:


Now, we will finish by doing addition and subtraction:



Our answer is
.
8x - 2y = -8
-5x + 2y = -1
3x = -9
x = -3