Given the toppings tomato lettuce onions mayo pickles and ketchup how many choices of 3 hamburger toppings are possible

Ineed with number 17 i don’t get it at alll

After t seconds, a ball tossed in the air from the ground level reaches a height of h feet given by the equation h = 144t-16t^2. after how many seconds will the ball hit the ground before rebounding?

If the ratio of sum of the first m and n terms of an ap is m2 : n2 , show that the ratio of its mth and nth terms is (2m − 1) : (2n − 1).