Help please! THANK YOU!

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%.

Find the cosine function that is represented in the graph.

Solve the inequality and graph 6j - 7 < 5