Billy is playing in his sandbox. He enjoys burying his toys in the sand. He has 3
dump trucks, 2 tractors, and 2 pickup trucks. Billy randomly selects a toy, buries it,
then chooses another. What is the probability that the first toy he picks is a tractor
and so is the second?

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?