You would use the following equation:
96 = 5x + x
There is a total of 96 marbles. The right side of the equation represents how many blue marbles are in the box. X is red marbles in the box, since we know that red marbles is 5 times x
Add the common variables:
96 = 5x + x
96 = 6x
To solve for red marbles isolate x. To do this divide 6 to both sides. Division is the opposite of multiplication and will cancel 6 from the right side and bring it to the left
96 ÷ 6 = 6x ÷ 6
16 = x
You have 16 marbles in the box
Hope this helped!
~Just a girl in love with Shawn Mendes