Ryan's marbles = x
Marie has 4 times less marbles then Ryan would have if he lost 15 marbles (it means he would have x-15)
So, Marie marbles = (x-15):4
If Ryan lost 75 marbles (it means he would have x-75), he would have 1 1/2 times as many marbles as Marie.
We got an equation: \(x-75=1\frac{1}2\cdot\frac{x-15}{4}\)
\(x-75=\frac{3}2\cdot\frac{x-15}{4}\)
Multiply both sides by 8: \(8x-8\cdot75=3\cdot(x-15)\)
\(8x-600=3x-45\)
Add 600 and subtract 3x on both sides: \(5x=555\)
Divide both sides by 5: \(x=111\)
Answer: Ryan have 111 marbles.
