Question 911886
The ground speed for jet traffic from Los Angeles to New York City can be about 100 mi/h faster than the ground speed from New York City to Los Angeles. This difference is due to a strong westerly wind at high altitudes. If "r" is a jet's ground speed from New York City to Los Angeles, write and simplify and expression for the round-trip air time. The two cities are about 2500 mi apart. 
***
let x=speed of jet in still air
c=speed of wind=50 mph(50 mph faster in one directiom and 50 mph slower in the other direction equals a difference of 100 mph between the two directions)
(x+c)speed of plane with the wind
(x-c)speed of plane against the wind
travel time=distance/speed
round trip air time={{{2500/(x+50)+2500/(x-50)}}}