Question 157616
Note that the total distance flown by both planes when they meet is 1260 mi. Therefore, one plane flies x mi, while the other plane flies 1260-x mi.
Using d=rt, where d refers to the distance traveled along one dimension, and r refers to the average speed, we have the following system of equations:

x=1.5r

1260-x=0.5(r+40)


Solve for r:

1.5r=1240-0.5r

3r=1240

r=620 mph (Answer), r=660 mph (Answer)