It takes a private airplane 8.75 hours to make the 2100-mile flight from
atlanta to los angeles and 5 hours to make the return trip. Assuming that the wind blows at a constant rate from Los Angeles to atlanta, find the airspeed of the plane and the wind rate.

i know that i have to use the d=rt formula....but when i get to the part where i make the formulas: (r+w)=2100 and (r-w)=2100.......i don't know what to do after that

2. ## d=rt

sydney0605, remember that it's d=rt, so rate = d/t, and we have

$(r-w)=\dfrac{2100}{8.75}=240$ and $(r+w)=\dfrac{2100}{5}=420$

This is just a system of linear equations (two equations for two unknowns) and can be easily solved by the addition method or the substitution method.

--Kevin C.

3. haha how do i set it up to do that substitution method?

4. ## Substitution

In the substitution method, you solve one of the equations for one variable in terms of the other variable, and substitute into the other equation. In this case, we can solve the first equation for w: $r - w = 240 \implies w = r - 240$
We then substitute r-240 for w in the second equation to get an equation of r only, which we solve for r. Plug this value into either equation and you can solve for w.

--Kevin C.

5. thank you very much kevin:-) that really helps a lot...i appreciate it