State which of the following sets of ordered pairs represent a function.

set a: (5, 2), (4, 3), (3, 4), (2, 5)

set b: (-1, -6), (0, 2), (1, 2), (3, 6)

set c: (2, 1), (4, 2), (2, 3), (8, 4)

a.

set c

b.

set b

c.

set a

d.

set a and set b

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?