Plz answer these plz i failing math

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%.

Evaluate the expression for the given value of the variable 7a - 4a for a =8

Which of the following three dimensional figures has a circle as it’s base