Can anyone help me with this? what is the value of b in the triangle shown below?

Right triangle lmn has vertices l(7, –3), m(7, –8), and n(10, –8). the triangle is translated on the coordinate plane so the coordinates of l’ are (–1, 8). (x, y) → (x + 6, y – 5) (x, y) → (x – 6, y + 5) (x, y) → (x + 8, y – 11) (x, y) → (x – 8, y + 11)