Assuming he works at a constant rate, the daily rate Mark rakes lawns in the fall is 40% of the daily rate he mows lawns in the summer.
Fall:
5 neighbors' lawns / 2.5 hours = 2 lawns per hour
Summer:
6 neighbours' lawns / 1.2 hours = 5 lawns per hour
2 x 100% / 5 = 40%
2 is 40% of 5