Ranch home is 2100 sq ft (70 x 30)

Question

Assume the climate yields 30in of rainfall per year.
Baths, showers, faucets use 40% of this water, of which 80% is recycled to the indoor garden (50 ft x 20 ft)

How much water in INCHES will the 50ft x 20 ft indoor garden receive per year from the recycled water?

I've tried
2100 x 2.5ft rain = 5280 cu ft
5280 cu ft x .40 x .80 = 1680 cu ft

am I on the right track?
where do I go from here?

Answer 1

50*20 = 1000 square feet

so we use 1680/1000 = 1.680 ft on pool
1.680 * 12 = 20.16 inches used

but there is an easier way

30 in * (2100/1000) * .4*.8
= 20.16 in