Q is 1 unit. P is 2 units (twice Q). R is Q + 80 = 1 unit + 80. S is a fixed 200 g. The four boxes total 960 g.<br><br>[[model:questions/solutions/q8379.png]]<br><br>• 1 + 2 + 1 = 4 units, plus 80 + 200 → 960 g<br>• 4 units → 960 − 280 = 680 g<br>• 1 unit (Q) → 680 ÷ 4 = 170 g<br>• P = 2 units → 2 × 170 = 340 g<br><br>Box P has a mass of 340 g.<br>Check: Q 170 + P 340 + R 250 + S 200 = 960 g. ✓