Ok what next helppp i need 2

Find the sum of the first 8 terms of the following sequence. round to the nearest hundredth if necessary.

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%.

Can someone me with this? i’m not sure what to put for my equations.