There are 18 cupcakes. how many 3/4 size servings can you make?

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%.

:malik received a $300 gift card from his grandparents and is using it only to pay for his karate lessons, which cost $30 per month. determine what amount, in dollars, remains on the card after 8 months.

Lines a and b are perpendicular. the equation of line a is y=13x+3. what is the equation of line b?