A cannon is fired from the top of a hill. the height h in feet of the cannonball is defined by the function h(t)=-16t^2+100t+280. Where t represents the time in seconds since the cannonball was fired. Part A. What is the maximum height of the cannonball? Do not enter units for your answer.

Part B. How long before the cannonball strikes the ground? Round to the nearest second.