First, figure out how much punch was left in the bowl before Mark refilled it by subtracting the 12 gallons he added from the bowl's total capacity: 16 - 12 = <<16-12=4>>4 gallons
Next, figure out how much punch was in the bowl before Sally came along: 4 + 2 = <<4+2=6>>6 gallons.
Next, figure out how much punch was in the bowl before Mark started to refill it: 6 - 4 = <<6-4=2>>2 gallons
Finally, multiply that amount by 2 to find out how much punch there was before the cousin drank half: 2 * 2 = <<4=4>>4 gallons
#### 4