Question

The altitude "a" (in feet) of a plane "t" minutes after liftoff is given by a -3400t+600. How many minutes after liftoff is the plane at an altitude of 21,000 feet?

Answer 1

21000 = 3400 t + 600 -> 21000 - 600 = 3400 t --> 20400 = 3400 t --> 20400/3400 = t --> t = 6  min

Answer 2

6 minutes

Explanation:

We are given that an altitude a (in feet) of a plane t minutes after liftoff is given by

`a=3400 t+600`

We have to find that how many minute after liftoff is the plane at an altitude of 21,000 feet.

`a=3400 t+600`

`3400 t=a-600`

Using subtraction property of equality

`t=(a-600)/(3400)`

Substitute the value of a then we get

`t=(21000-600)/(3400)`

`t=6` minutes

Hence, 6 minutes after liftoff is the plane at an altitude of 21,000 feet.