1 mile = 5280 feet.
Convert the dimensions to feet:
10 miles = 5280 x 10 = 52,800 feet
30 miles = 5280 x 30 = 158,400 feet
Multiply together to get the area:
52,800 x 158,400 = 8,363,520,000 square feet.
1 inch = 1/12 of a foot.
Multiply the area by 1/12 for the volume of rain:
8,363,520,000 x 1/12 = 696,960,000 cubic feet.
