Question 136864
Do me a favor please.  Stop typing your questions in ALL CAPS.  It is rude, annoying, hard to read, and is the electronic equivalent of shouting.


The speed of the plane in still air: {{{r}}}
The speed of the wind {{{r[w]}}}
The speed of the plane against the wind: {{{r-r[w]}}}
The speed of the plane with the wind: {{{r+r[w]}}}


Distance equals rate times time:  {{{d=rt}}}, but this can be solved for rate: {{{r=d/t}}}


For the trip against the wind:  {{{r-r[w]=780/2=390}}}
For the trip with the wind: {{{r+r[w]=780/1.5=520}}}


Add these two equations:
{{{(r+r[w])+(r-r[w])=910}}}
{{{2r=910}}}
{{{r=455}}}


Check:
If r is 455, then r[w] has to be 455 - 390 = 520 - 455 = 65.


So, against the wind, the plane goes 780 miles at 390 mph -- trip takes 2 hours
With the wind, the plane goes 780 miles at 520 mph -- trip takes 1.5 hours.