In economics, marginal cost is the additional expenditure or cost you incur when you buy another more quantity of the product. When Allison bought the 1minus−color application, she spent a total of $130.
$35 + $95 = $130
When she upgraded to 3minus-color application, her cost now increased to
$175 + $40 = $215
Now, as mentioned, marginal cost is the additional cost incurred when buying one more quantity of the same product. Therefore, marginal cost = Δcost/Δquantity. Thus,
Marginal Cost = ($215-$130)/(3-1)
Marginal Cost = $42.5
The marginal cost is $42.5 per color application.