First find the volume of the pool by multiplying the length by the width by the height: 10 ft * 8 ft * 6 ft = <<10*8*6=480>>480 cubic feet
Then divide the volume of the pool by the number of cubic feet one quart of chlorine can sterilize: 480 cubic feet / 120 cubic feet/quart = <<480/120=4>>4 quarts
Then multiply the number of quarts Gary needs to buy by the price per quart to find out how much money he spends: $3/quart * 4 quarts = $<<3*4=12>>12
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