The value of √-9 is not -3 because...?

This is a table of values that follows a given rule or function. each output comes from the input being applied to the rule.

The green family is a family of six people. they have used 4,885.78 gallons of water so far this month. they cannot exceed 9,750.05 gallons per month during drought season. write an inequality to show how much water just one member of the family can use for the remainder of the month, assuming each family member uses the same amount of water every month.

How do you use the elimination method for this question? explain, because i really want to understand!