They decided to hold the party in their backyard. They have 20 sets of tables and each set has 3 chairs. There are also 11 chairs extra. How many chairs do they have for the guests?
There are 20 sets of tables and each set has 3 chairs. 
That means there are 60 chairs in total from the sets of tables. 
There are also 11 chairs extra. 
That means there are 71 chairs in total for the guests.