Answer:
300 g or 0.3 kg
Explanation:
23 kg - 500g = 22.5 kg
each can of biscuits weighs 22.5 ÷ 15 = 1.5 kg
if the box Q weighs 12.3kg when there's 8 box of biscuits then
8 × 1.5 = 12 kg is the weight of biscuits and the remaining 300 g is box Q's weight