What is 2x= 10
what is x

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%.

On a piece of paper graph f(x)=5•(0.4)^x

Can someone me out here number 4 plz