Answer:
Speed of airplane in still air = 630 mile per hour
Speed of wind = 70 miles per hour.
Step-by-step explanation:
Let speed of plane in still air =
miles/hour
Let speed of wind =
miles/hour
Speed of airplane with the wind can be given by =
miles/hour
Speed of airplane against the wind can be given by =
miles/hour
Distance of the trip = 2800 miles
Time taken by airplane to travel with the wind = 4 hours
Speed of plane with wind =

Distance of the return trip (same trip distance) = 2800 miles
Time taken by airplane to travel with the wind = 5 hours
Speed of plane with wind =

So, we have the system of equations:
A)

B)

Using elimination method to solve.
Adding equation A to B to eliminate
.

+

We get

Dividing both sides by 2.

∴

Using
in equation A to find


Subtracting both sides by 630

∴
Speed of airplane in still air = 630 mile per hour
Speed of wind = 70 miles per hour.