13. On weekends, as part of his exercise routine, Carl goes for a run, partly C on paved trails and partly across rough terrain. He runs at 10 km/h on
the trails, but his speed is reduced to 5 km/h on the rough terrain. One
day, he ran 12 km in 1.5 h. How far did he run on the rough terrain?

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?