A = 6 units, C = 2 units. A has 84 ml more than C, which is the 4-unit difference.<br><br>[[model:questions/solutions/q4502.png]]<br><br>• A − C → 6 units − 2 units = 4 units → 84 ml<br>• 1 unit → 84 ÷ 4 = 21 ml<br>• B → 7 units = 7 × 21 = 147 ml<br><br>Container B has 147 ml of water.<br>Check: A 126, C 42; 126 − 42 = 84; B = 7 × 21 = 147. ✓