Jill mowed lawns for 3 hours and earned $7.20 per hour. then she washed windows for 4 hours and earned $6.75 per hour. what were jill's average earnings per hour for all 6 hours?

Actually, she worked for seven hours, so I'll solve for that.

7.20 x 3 = 21.6

6.75 x 4 = 27

21.6 + 27 = 48.6

48.6 /2 = 24.3

Her average should be $24.3  If she did work six hours, just multiply 6.75 x 3 and do what I did.