Given: X: The blue marbles. 3X: The red marbles. A box contains 144 marbles. SOLVING: X + 3X = 144 4X = 144 X = $\frac{144}{4}$ X = 36 ===> The blue marbles. If there are 3 times as many red marbles as there are blue marbles: 3(36) = 108 ===> The red marbles. SOLUTION TESTING: $36+108=144$ $\boxed{144}=\boxed{144}\quad\checkmark\ The\ value\ is\ correct.$ GOOD LUCK...!!!