An example on how to solve age problems in consecutive integers

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%.

Select the two pairs of figures that are similar.

Which expression is equivalent to 64 - 9x^2?