The band played 5 + 7 = <<5+7=12>>12 songs in their first two sets.
They have 30 - 12 = <<30-12=18>>18 songs left for the third set, fourth set and encore.
Since they played 2 songs in the encore, they have 18 - 2 = <<18-2=16>>16 songs to play on the third and fourth sets
They will play 16 / 2 = <<16/2=8>>8 songs on average over the third and fourth sets.
#### 8