A diving board is 5 feet above the water level of the pool. A swimmer steps off the board into the water. The function d= -16x +5 gives the distance d of the swimmer's feet above the water level after x seconds.

a. When does the swimmer's feet hit the water?

b. When will the swimmer's feet be 4 feet below the water level?

c. The high diving board is 15 feet above the water level of the pool. How could you translate the function d = -16x + 5 to adjust for the height of the high diving board?

plss help.. show all work thank you