Whats 4/5 of 3/4 and whats 2/3 of 1/4

You paid 28.00 for 8 gallons of gasoline. how much would you pay for 15 gallons of gasoline?

Dawn is selling her mp3 player for 3 4 of the original price. the original price for the mp3 player was $40. how much is she selling her mp3 player for?

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?