They decided to hold the party in their backyard. They have 39 sets of tables and each set has 10 chairs. There are also 23 chairs extra. How many chairs do they have for the guests?
There are 39 sets of tables and each set has 10 chairs. 
That means that there are 390 chairs in total. 
There are also 23 chairs extra. 
That means that there are 413 chairs in total.