Answer:
75 minutes
Explanation:
First cook 40 and 45 min dishes on separate burners. Then after 40 min put 35 min dish to be cooked on that burner. This will take 75 minutes time.
On second burner put firstly 15 min and then 10 min dish or vice versa as it doesn't matter. This second burner will take 70 minutes which is less then first one.