Answer:
63 gallons.
Step-by-step explanation:
If 30% of water is used outdoors, that leaves 70% to be used indoors. Since an average person uses 90 gallons, all we need to do is fine 70% of 90 gallons. To do this, we have to multiply 90 by 0.7:
90 * 0.7 = 63
In conclusion, 63 gallons of water are used indoors.