First find what percent of the seaweed can be used for something besides starting fires: 400 pounds / 2 = <<400/2=200>>200 pounds
Then divide that amount by 4 to find the amount that's eaten by humans: 200 pounds / 4 = <<200/4=50>>50 pounds
Then subtract that amount from the 200 pounds to find how much is eaten by livestock: 200 pounds - 50 pounds = <<200-50=150>>150 pounds
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