a= x+y ÷2 solve for y
a = x + y ÷ 2We multiply both sides by 2That is,2 × a = x + y ÷ 2 × 2We get2a = x + ySince we are solving for y, we move x to the other side of the equation So we have2a - x = yTherefore, y = 2a - x