Let the total no days to require to build the house with 45 men be X.
first 40 days, 45 men worked, so the total work done is 40*45
the job is finished 5 days ahead of 60 days, nothing but 60-5=55 days

so for 15 days 45+30 = 75 men worked.

Total work done =(40*45) + (15*75) = 45 men worked for X days,
45*X = (40*45) + (15*75)
solve for x, X will be 65. that means 45 men would have completed the job in 65 days. so 5 days more than planned.

Regards,
Kalyan.