The ratio of red to blue to yellow marbles is 3 : 2 : 6. Red marbles are 3 units and equal 36.<br><br>[[model:questions/solutions/q4485.png]]<br><br>• 3 units → 36 red marbles<br>• $$\frac{1}{1}$$ unit → 36 ÷ 3 = 12<br>• Blue marbles → 2 units → 2 × 12 = 24<br><br>There are 24 blue marbles.<br>Check: Yellow = 6 × 12 = 72. Ratio check: 36 : 24 : 72 = 3 : 2 : 6. ✓