The "key" to this is to recognize that the two lines have to be the same length, they put the drawing on it's side to make it harder to see that. :/ But another way to see this is that it's an isosceles triangle and you know the two legs that they are asking us about have to be the same length, knowing that.. we can set the two expression equal to each other
3x - 10 = 2x
now solve for x
3x - 10 -2x = 2x - 2x ( subtracting 2x from both sides )
