Algebra 2 functions. Show work

Adepartment store purchases screen-printed t-shirts at a cost of $5 per shirt. they mark up the price 150% (making the selling price 250% of the store's purchase price) and put them on the sales floor. every month that a t-shirt doesn't sell, the store reduces the selling price by 25%.

In the figure shown below, m < 40 and ab =8. which equation could be used to find x?

What is always true when two whole numbers are subtracted?