Roger originally had 4 cans of silly string + 2 can he gave to his brothers = <<4+2=6>>6 cans.
Since his friends received the same amount as Roger did originally, 3 friends x 6 cans of silly string = <<3*6=18>>18 cans.
Michelle started with 6 cans that went to Roger + 18 cans that went to his friends = <<6+18=24>>24 cans of silly string.
#### 24