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2 Answers

Hello Mishonta.
 
Vivian's generous reply is very correct. I would just like to show you the way I would set up the solution. I like to use descriptive variable names. And I like to take lot's of paper space to setup these things. Even at the risk of looking repetitious. I encourage all my students to be work in this way. It either cuts down on dumb mistakes, or else it makes mistakes easier to track down.
 
Sp = still air Speed of the plane
Sw = the Speed of the wind
 
Sp + Sw = 480  ... in this case the wind speeds it up.
Sp  - Sw = 400  ... in this case the wind slows it down.
 
We can solve for one of the unknowns, by adding the equations:
 
    Sp + Sw = 480
+ (Sp - Sw = 400)
-----------------
  2Sp  + 0 = 880
 
Sp = 880/2
Sp = 440
 
You can use this value in either equation, above, to find that the wind Speed, Sw, is 40.
 
Cheers!
Hi Mishonta;
x=still air speed
wind must be 40 miles/hour because the difference between 480 and 400 is 80, divided by 2 this is 40.
x-40=480
x+40=400
still air speed is 440 miles/hour