A student has an 80 g sample of a radioactive material that has a half-life of 20 seconds. How much material will he have left after 60 seconds? A.
10 g

B.
20 g

C.
40 g

D.
5 g

An astronaut on the moon throws a baseball upward. the asatronaut is 6ft, 6in. tall, and the initial velocity of the ball is 30ft per second. the heigh s of the ball in feet is given by the equation s = -2.7^2 + 30t + 6.5, where t is the number of seconds after the ball was thrown. after how many seconds is the ball 16ft above the moon's surface?