Chelsea baked 4 batches of cupcakes x 20 minutes each = <<4*20=80>>80 minutes of baking.
She iced 4 batches of cupcakes x 30 minutes each = <<4*30=120>>120 minutes.
It took Chelsea 80 + 120 = <<80+120=200>>200 minutes to make the cupcakes for the bake sale.
#### 200