It is the rainy season in central Texas.  It rained for 7 hours on Monday at a rate of 1 inch per hour.  On Tuesday, it rained for 4 hours at a rate of 2 inches per hour, and on Wednesday, it rained for 2 hours at a rate of twice that of the previous day.  What is the total combined rainfall, in inches, for these three days?
Please reason step by step, and put your final answer within \boxed{}.
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