For the first 30 minutes, 3*2=<<3*2=6>>6 cups of water came out.
For the next 30 minutes, 3*2=<<3*2=6>>6 cups of water came out.
For the next hour, 6*4=<<6*4=24>>24 cups of water came out.
A total of 6+6+24=<<6+6+24=36>>36 cups of water came out.
Shawn had to dump water which left 36/2=<<36/2=18>>18 cups of water.
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