Solution:
1) Producer surplus per month = no of persons renting the house multiply ( price charged by landord from each person - price of the room that landlord was willing to rent for)
producer surplus per month = 4 multiply ( 550 - 500) = 4 multiply 50 = $200
2) Consumer surplus per month = (price that i am willing to pay - price at which room is leased) + (price 1st friend is willing to pay - price at which room is leased) + (price 2nd friend is willing to pay - price at which room is leased) + (price 3rd friend is willing to pay - price at which room is leased) = ( $580 - $550) + ( $550 - $550) + ($610 - $550) + ($610 - $550) = $30 + $0 + $60 + $60 = $150
3) total surplus per month = Producer surplus per month + Consumer surplus per monrth = $200 + $150 = $350