Way 1: Substitute y = 3 into the equation to find that
5x - 9(3) = 12
and then solve to find that .
Way 2: Solve the original equation for x to get a formula that gives x in terms of y:
Then substitute 3 for y to find that
Either way, we do the same amount of work. The only difference is whether we rearrange things before or after we substitute in numbers. It's the same way you get your pants on whether you put your right leg or left leg into them first. Or maybe you're one of those people who leaps into the air and puts them on both legs at once. We've heard about you.