Question 627903
each load takes 20+15+20=55 minutes each load
add 15 minutes for each truck return trip.

8*60=480 minutes
9*55=495 minutes
one truck can't do it even without considering the return trip
two trucks cant do it.
4 trips for one truck
20+15+20+15=70
20+15+20+15=70
20+15+20+15=70
20+15+20=55
70+70+70+55=210+55=265

 and 5 trips for 
20+15+20+15=70
20+15+20+15=70
20+15+20+15=70
20+15+20+15=70
20+15+20=55
70+70+70+70+55=280+55=325
325/60 in a little over 5 hours