Question 1076780
Let s be the speed of the plane in still air. Then:
600/s+15 + 600/s-15=9
600(s-15)+600(s+15)=9s²-2025
9s²-1200s-2025=0
3s²-400s-675=0
(3s+ 5)(s-135)=0
s=-5/3 or 135
Ignoring the negative result, we get the speed of the plane in still air to be 135 mph. &#9786;&#9786;&#9786;&#9786;