Answer:
• y=150+7x
,
• 8 months
Explanation:
• The purchase cost of the home security system = $150.
The monthly service cost = $7.
If the number of months the security system is in operation = x
• Then, the service cost for x months = $7x
Therefore, the cost of owning the system for x months is given by the equation:

When the amount spent, y = $200

We solve for x in order to estimate how many months you will have owned the system.

By the time you've spent $200 on home security, you will have owned the system for 8 months.