Pirate Rick digs at a rate of 8 feet of sand per 4 hours, or 8/4=<<8/4=2>>2 feet per hour.
Of the 8 feet of sand that were initially on top of the treasure, the storm washed 8/2=<<8/2=4>>4 feet of sand away.
Thus, after the storm and the tsunami, the treasure was buried beneath 8-4+2=<<8-4+2=6>>6 feet of sand.
Digging at a rate of 2 feet per hour, Pirate Rick could uncover his treasure in 6/2=3 hours.
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