Hi Tamara!

We will need to model the scenario with 2 separate equations because we need to solve for two unknowns. Let's say that the **Bennett family uses their sprinkler for B hours** and the **Hill family uses theirs for H hours**.

Equation #1

- The problem tells us that the Bennett's sprinkler uses water at a rate of 25L per hour; so we can say that in
**B hours, the Bennet family uses 25B liters of water.** - We're told that the Hill family's sprinkler uses 15L of water per hour; so we can say that in
**H hours, the Hill family uses 15H liters of water.** - The problem states that,
**in total, the two families use a combined total of 1075L** - Putting this all together, we can say
**25B + 15H = 1075**(equation #1)

Equation #2

- Since we're told that the two families use the sprinklers for a combined
**total of 55 hours, we can say that B+H=55**

Solving:

We can solve by substitution or elimination. I'll use substitution by solving equation #1 for H, and then subbing that result into equation #2.

- Solve equation #2 for H: B+H=55 -> H=55-B
- Plug H=55-B into equation #1: 25B+15H=1075 -> 25B+15(55-B)=1075 -> 25B+825-15B=1075 -> 10B=250 ->
**B=25 hours** - Use B=25, to solve for H in either equation: B+H=55 -> 25+H=55 ->
**H=30 hours**

And you're done!