First find the total weight of the carrots: 4 pounds * 2 = <<4*2=8>>8 pounds
Now add the total weight of each item: 6 pounds + 8 pounds + 4 pounds = <<6+8+4=18>>18 pounds
Now subtract the total weight of the groceries from the bag's weight limit: 20 pounds - 18 pounds = <<20-18=2>>2 pounds
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