The builder purchased 7 boxes * 11 bolts = <<7*11=77>>77 bolts.
He used 77 bolts - 3 left over = <<77-3=74>>74 bolts for the project.
The builder purchased 3 boxes * 15 nuts = <<3*15=45>>45 nuts.
He used 45 nuts - 6 left over = <<45-6=39>>39 nuts for the project.
Total for the project he used 74 bolts + 39 nuts = <<74+39=113>>113 nuts and bolts.
#### 113