Please help need answers

Easy points boii. read it. ya. fresh

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%.

Express the following as a function of a single angle. cos(60) cos(-20) - sin(60) sin(-20)