The marginal cost refers to the cost of producing one additional unit or serving one more customer.
In this case, we have to determine the additional cost of Jacob ordering a burrito instead of a taco. As Mason chose the tacos and they agreed to split the lunch bill evenly, if Jacob decides to eat the tacos, the cost for each of them is:
$3+$3=$6/2= $3
If Jacob decides to eat the burrito:
$3+$5= $8/2= $4
So, the marginal cost to Jacob ordering a burrito is:
