I NEED HELP! I AM THE WORST AT MATH Jonah is playing a video racing game called Checkpoint. The speed of Jonah’s car is recorded four times during one lap. At the first checkpoint, his speed is 80 miles per hour. At the second checkpoint, his speed has reduced by 5%. At the third checkpoint, Jonah’s speed has increased by the speed from the previous checkpoint. At the fourth checkpoint, his speed decreased by 20% compared with the third checkpoint. What is Jonah’s net change in speed between the first and fourth checkpoints?
A. 4
B. -4
C. 15
D. -15

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?