Question 332548
With the wind, we add the two rates. Against the wind, we subtract them.

Let rp=rate of plane and rw = the rate of thr wind.

With the wind:

Since d=rt, we have 1400=5(rp+rw)

Against the wind:

we have 1400=7(rp-rw)

These reduce to 

rp+rw=280
rp-rw=200

Now, from the first equation we have rp=280-rw

Sub into the second equation:

280-rw-rw=200

280-2rw=200

rw=40=rate of wind.

That means the rate of the plane, rp, is 240.