The scale is balanced. This is the case if the distances * weights are the same on both sides of the scale: (A + B) * weigth 1 + B * weight 2 = C * weigth 3 + (C + D) * weight 4.
(? + 180) * 10 + 180 * 2 = 200 * 8 + (200 + 160) * 6.
==> (? + 180) * 10 + 360 = 3760.
==> (? + 180) * 10 = 3760 - 360.
==> (? + 180) = 3400 / 6.
==> ? + 180 = 340.
==> ? = 340 - 180.
==> ? = 160.