c = 5n
each notebook is 5 dollars. so we multiply each notebook Carmen buys by 5 to find what she has to pay in total.
it's like if you eat 2 chocolates, and each contain 100 calories, you would be eating 200 calories total. the equation for that scenario would use the same logic:
totalCalories = 100*numberOfChocolates
since 100 is the number of calories in 1 chocolate.
78.59 is the mean