That is the "order of operations" when you are performing a calculation.
When you are solving an equation, you have to remember that you are "backing" out so everything runs in reverse.
For example, if and had to calculate y for a given value of x (you know x and want to find y), you would use "BODMAS" or "PEMDAS" (P for parentheses instead of B for brackets- which you can remember as "Please excuse my dear aunt Sally"). Since the "vinculum" (the line between numerator and denominator) counts as a "bracket" or "parentheses" you first MULTIPLY 2 by x, the SUBTRACT 1, finally DIVIDE by 3.
But when you want to solve the equation- you know y and want to find x, just the opposite of the above- you do the opposite; the opposite of each operation in the opposite order. First you MULTIPLY both sides of the equation by 3 then ADD 1 to both sides, finally DIVIDE both sides by 2.