Work backwards from the $15 left. The toy takes 1/4 of the remainder after the watch; what remains is 3/4 = $15.<br><br>[[model:questions/solutions/q4341.png]]<br><br>• Left $15 = 3/4 of remainder after watch<br>• 1/4 of remainder = Toy → $15 ÷ 3 = $5<br>• Remainder after watch → $5 × 4 = $20<br>• Remainder = 2/3 of total → 1/3 = $10<br>• Watch → 1/3 × total = $10<br><br>Rex spent $10 on the watch.<br>Check: Watch $10, remainder $20. Toy = 1/4 × $20 = $5. Left = $20 − $5 = $15. Total = $30. ✓