Understanding Equivalent Equations in Algebra - ThoughtCo 03/10/2019 · To find the point where prices are equal, let "x" remain the number of shirts, but set the two equations equal to each other. Solve for "x" to find how many shirts you'd have to buy: 6x + 12 = 7.5x + 9; 6x - 7.5x = 9 - 12 (subtracting the same numbers or expressions from each side)-1.5x = -3; 1.5x = 3 (dividing both sides by the same number, -1) x = 3/1.5 (dividing both sides by …