Please help, i am being timed and i am stuck. Which of the following relations represent functions? Select ALL that apply.​

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%.

What is the measure of ac? 5 units 13 units 26 units 39 units 3x- 2b 6x + 9

Ijust need these 2 questions answered (the second pic is just confirmation i'm not confident in that answer)