The storybook is one unit plus an extra $2; the eraser packet is one unit. Together they make $12.<br><br>[[model:questions/solutions/q2424.png]]<br><br>• 2 units + $2 → $12<br>• 2 units → $12 − $2 = $10<br>• 1 unit → $10 ÷ 2 = $5<br><br>The packet of erasers costs $5.<br>Check: $5 (erasers) + $7 (storybook) = $12. ✓