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?
How to solve this?