Sophie has 4 - 1 = <<4-1=3>>3 boxes of donuts left.
The total number of pieces of donuts that she has is 3 x 12 = <<3*12=36>>36.
She gave 12 / 2 = <<12/2=6>>6 donuts to her sister.
Therefore Sophie was left with 36 - 6 = <<36-6=30>>30 donuts after giving her sister.
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