Mike can cut a 40 foot by 20 foot yard with a push mower in 25 minutes. At this rate, how many more minutes would it take him to cut a 40 foot by 30 foot yard?

Area of the yard is 40.20 = 800sq ft

time taken = 25 mins

time taken to mow 1sq ft = 25/800 mins

time taken to mow 40.30 = 1200sq ft = (25.1200) / 800 = 371/2 mins

thus the extra time taken will be 371/2-25 = 121/2 mins