The linear equation that models the cost for having x additional family members added is:
c(x) = $75 + $10.99*x
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How to get the linear equation?</h3>
Here we know that the plan has a fixed price of $75 plus $10.99 for each family member added beyond the primary account holder.
Then if there are x family members added, the cost will be:
$75 + $10.99*x
Then the linear equation that models the cost for having x additional family members added is:
c(x) = $75 + $10.99*x
If you want to learn more about linear equations:
brainly.com/question/1884491
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I hope this helps you
3x-25=6x-80
6x-3x=80-25
3x=55
x =55/3