A parking lot has two entrances. Cars arrive at Entrance 1 according to a Poisson Probability Distribution at an average of three per hour and at Entrance 2 according to a Poisson Probability at an average of four per hour. What is the probability that a total of three cars will arrive at the parking lot in a given hour. What is the probability that a total of three will arrive at the parking in a given hour? Assume that the numbers of cars arriving at the two entrances are independent. [Hint: This is hard but not as hard as you think].

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?