a. Benjamin threw a rock straight up from a cliff that was 100 ft above the water. If the height of the rock h, in feet, after t seconds is given by the equation h=16t^2+60t+100, how long will it take for the rock to hit the water?

b. A boat traveled downstream a distance of 75 mi and then came right back. If the speed of the current was 8 mph and the total trip took 5 hours,find the average speed of the boat relative to the water.