1. **State the problem:** Fiona has a box with 12 identical chocolates. The total weight of the box plus all chocolates is 294g. After eating 7 chocolates, the total weight of the box plus remaining chocolates is 210g. We need to find the weight of the box. 2. **Define variables:** Let $b$ be the weight of the box in grams. Let $c$ be the weight of one chocolate in grams. 3. **Write equations based on the problem:** - Total weight initially: $$b + 12c = 294$$ - Total weight after eating 7 chocolates (5 chocolates left): $$b + 5c = 210$$ 4. **Solve the system of equations:** Subtract the second equation from the first: $$ (b + 12c) - (b + 5c) = 294 - 210 $$ $$ b - b + 12c - 5c = 84 $$ $$ 7c = 84 $$ $$ c = \frac{84}{7} = 12 $$ 5. **Find the weight of the box:** Substitute $c=12$ into the second equation: $$ b + 5(12) = 210 $$ $$ b + 60 = 210 $$ $$ b = 210 - 60 = 150 $$ **Answer:** The weight of the box is $150$ grams.