You ultimately need to determine the difference in speed for the average miles per hour in still air vs the actual speed based on the distance travelled in the time specified, and then you will have the answer to the equation.

So, it should flow as follows:

Jet flew 240 miles and back: 240 x 2 = 480

1 hour and 10 minutes = 70 minutes

Determine the speed per minute: 480/70 = 6.587

Determine the speed per hour: 6.857*60 (minutes in an hour) = 411.42

Average speed in still air (420) - Average speed in wind (411) = 9

Answer: wind speed is 9 miles per hour