She spends $150 for X number of t-shirts for $10 each, which makes it $10x ( the total cost of X number of t-shirts ) & Y number of jeans for $20 each, which makes it $20x ( total cost of Y number of jeans )
$150 - $10x - $20y ( the amount she is left with )
In order to find the amount of t-shirt she can buy with the amount she is left with we divide it by $10
150-10x-20y/10
10(15-x-2y)/10
15-x-2y
Answer: 15-x-2y
