Of the students living in the dormitories at aa€‹ university, 65% live at the westa€‹ hall, and the rest at the south tower. A sandwich shop randomly mails a coupon for a free sandwich to 24% of those at the westa€‹ hall, and to 19% of those living at the south tower. Let D be the event that the person receive a coupon, E1 be the event that the person is living in the westa€‹ hall, and E2 be the event that the person is living in the south tower. A student living in a dormitory is randomly chosen. Required:
Find the probability that this person received a coupon. Also write an expression that models the probability.

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?