Which pair of equations generates graphs with the same vertex?
a. y = –(x + 4)2 and y = (x – 4)2
b. y = –4x2 and y = 4x2
c. y = –x2 – 4 and y = x2 + 4
d. y = (x – 4)2 and y = x2 + 4

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?