Can you give me some step-by-step instructions for this math problem: The county fair was hosting a pumpkin contest to see who could grow the biggest pumpkin in pounds.  Brad entered his pumpkin with a weight of 54 pounds.  Jessica's was half the weight of Brad's.  Betty's pumpkin weight 4 times the amount of Jessica's pumpkin.  What is the difference between the heaviest and lightest pumpkin in  pounds?