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.
(160 + 160) * 2 + 160 * 2 = 140 * ? + (140 + 200) * 2.
==> 960 = 140 * ? + 680.
==> 960 - 680 = 140 * ?.
==> ? = 280 / 140.
==> ? = 2.