A baseball player hits a baseball into the air with an initial vertical velocity of 78 feet per second. The player is 6 feet tall, and the height of the ball when hit is half his height. At what two different times does the baseball have a height of 84 feet above the ground? Do not round your answer. (Hint: -54 is a helpful number)

Aspacecraft can attain a stable orbit 300 kilometers above earth if it reaches a velocity of 7.7 kilometers per second. the formula for a rocket's maximum velocity v in kilometers per second is vequalsminus0.0098tplusc ln upper r, where t is the firing time in seconds, c is the velocity of the exhaust in kilometers per second, and r is the ratio of the mass of the rocket filled with fuel to the mass of the rocket without fuel. find the velocity of a spacecraft whose booster rocket has a mass ratio of 20, an exhaust velocity of 2.1 km/s, and a firing time of 15 s. can the spacecraft achieve a stable orbit 300 km above earth?