A local store sells boxes of pens. The cost of a box of pens and the number of pens in the box are related. You need 39 pens. Identify the independent variable in the relationship.
What is the independent variable?
A.
The cost of a box of pens
B.
The cost of each pen
C.
The number of boxes of pens you need
D.
The cost of the boxes of pens you need
E.
The number of pens in the box
F.
The number of pens you need

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?