This is a tough one, I already know that GD is congruent to FG, so in order to find GD, you use pythagorean theorem, which will be GD^2+15^2=17^2 or 17^2-15^2=GD^2, which is 64 and square root tht is 8. Next, given that CD=15 and CD is Congruent to BC, this meant that BG must be congruent to GD and therefore BG must equal 8
