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           Shane, 
          Since you want the volume in cubic yards, (yards   yards   yards) you need all three dimensions in yards. There are 3 feet in a yard and 36 inches in a yard and hence 
          
            4 inches is 4/36 yards 
               
              18 feet is 18/3 yards and 
               
              27 feet is 27/3 yards 
             
          Thus the volume is 
          
             4/36    18/3    27/3 = 6 cubic yards. 
             
          Penny  
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