The basses take 3*4=<<3*4=12>>12 strings
He restrings 2*3=<<2*3=6>>6 normal guitars
That takes 6*6=<<6*6=36>>36 strings
He restrings 6-3=3 guitars with 8 strings
So that uses 3*8=<<3*8=24>>24 strings
So he uses 12+36+24=<<12+36+24=72>>72 strings
#### 72