At each feeding Billy serves 4 horses x 4 pounds of oats/horse = <<4*4=16>>16 pounds/feeding
Each day Billy uses 16 pounds of oats/feeding x 2 feedings/day = <<16*2=32>>32 pounds of oats/day
Triple that amount to find the amount of oats needed to feed the four horses for three days: 32 pounds of oats/day x 3 days = <<32*3=96>>96 pounds
#### 96