Because K is the midpoint of JL and JK = 18, KL must also equal 18. So the equation would be 3x - 15 = 36 because you add 18 + 18. You then add 15 to both sides to get 3x = 51. Then you divide by 3 on both sides to get x = 17.
It means that you take a triangle and make another one but this time it is not the same size of the first one but the same shape. In other words make it bigger or smaller than the first one.
