Find the speed of the plane in still air?

Question

flying to Kampala with a a tailwind a plane averaged 158km/h.on the return trip the plane only averaged 112km/h while in the same wind.Find the speed of the plane in still air

Answer 1

Let still air speed = Vsa

 

Let wind speed = Vw

 

So, with a tailwind:     Vsa + Vw = 158

 

And with a headwind: Vsa - Vw = 112

 

Adding the equations:       2Vsa = 270

 

Therefore, Vsa = ________. I'm sure you can finish this problem.