Question 604449
x =  speed of plane in still air (in mph)
w = wind speed (in mph)
The plane's speed with tail wind is x+w.
The plane's speed going against the wind is x-w
1(x+w)=300 <---> x+w=300
2(x-w)=300 <---> 2x-2w=300
We have a system of two equations and many ways to solve it.
We can multiply the first equation times 2 and add the second equation to get
2(x+w)+2x-2w=2(300)+300 ---> 2x+2w+2x-2w=600+300 ---> 4x=900 --> 4x/4=900/4 ---> x=225
The speed of the plane in still air is 225 mph