V =
h
1. Find the radius.
8/2 = 4
2. Square the radius.
= 16
3. Multiply that by pi.
3.14 * 16 = 50.24
4. Multiply that by the height.
50.24 * 20 = 1004.8
5. Now find 60% of that.
1004.8 * 0.6 = 602.88
V = 602.88
Honestly, it's been a while since I've done this, but I believe this is the answer.
Use a proportion.
Let A = water used in household A.
Let B = water used in household B.
A to B = 13 to 5
A = 260 gal
260 to B = 13 to 5
260/B = 13/5
13B = 5 * 260
B = 100
A + B = 260 + 100 = 360
The total is 360 gallons.