This year, Kyle was only able to pick 12/2 = <<12/2=6>>6 roses.
He wants to give his mother 12 x 2 = <<12*2=24>>24 roses.
He still needs another 24 - 6 = <<24-6=18>>18 roses.
He would have to spend 18 x 3 = $<<18*3=54>>54.
#### 54