Answer:
- Sarah should not join the Mug Club as it will cost her more when buying 6 cups of coffee than if she wasn't a member of the Mug Club.
- The Mug Club costs the same as purchasing coffee without the Mug Club membership when 8 cups of coffee are purchased.
- The total cost is $18.00.
- You would need to purchase more than 8 cups of coffee in order to make the Mug Club the better deal.
Explanation:
Define the variables:
- Let x be the number of cups of coffee Sarah purchases.
- Let y be the total cost (in dollars).
If a cup of coffee costs $2.25, the equation to represent the total cost of purchasing x cups of coffee would be:

If Sarah joins the Mug Club, she has to pay $8.00 for a mug but then gets a dollar off each cup of coffee. Therefore, each cup of coffee would cost $1.25.
Therefore, an equation for the total cost of purchasing x cups of coffee when a member of the Mug Club would be:

To find the cost of purchasing 6 cups of coffee, input x = 6 into the two equations:


As $15.50 is greater than $13.50, Sarah should not join the Mug Club as it will cost her more when buying 6 cups of coffee than if she wasn't a member of the Mug Club.
To find when the Mug Club costs the same as purchasing coffee without the Mug Club, substitute the first equation into the second equation and solve for x:



Therefore, the Mug Club costs the same as purchasing coffee without the Mug Club membership when 8 cups of coffee are purchased.
To find the total cost, substitute x = 8 into one of the equations:

Therefore, the total cost is $18.00.
To calculate how many cups of coffee you would need to purchase in order to make the Mug Club the better deal, set the equation for the Mug Club less than the equation without the Mug Club and solve for x:




Therefore, you would need to purchase more than 8 cups of coffee in order to make the Mug Club the better deal.