Two jet planes simultaneously started travelling in opposite directions from the same airport. four hours later they were 3800 miles apart. if one plane traveled 80 miles per hour faster than the other, what was the speed of each plane?

Represent the speed of the first plane by f and that of the second plane by s.
Then 4f+4s = 3800 miles, or f+s = 950 miles.  Thus, f + (f + 80) = 950, so that
2f = 870, and f = 435 mph.  Then s = (435+80)mph, or 515 mph.

The first plane flew at 435 mph and the second at 515 mph.

Check:  (4 hours)(435 mph) + (4 hours)(515 mph) = 3800 mi (as expected)