9514 1404 393
Answer:
405 mph; 325 mph
Explanation:
The total of their speeds is ...
2920 mi/(4 h) = 730 mi/h
If s represents the speed of the slower plane, then we have ...
s + (s+80) = 730
2s = 650 . . . . . . . subtract 80
s = 325 . . . . . . . divide by 2
s+80 = 405 . . . find the faster speed
The speeds of the planes are 405 mi/h and 325 mi/h.