The marginal costs are:
The first pair: $7
The third pair: $1
The fifth pair: $2
To calculate the marginal cost, you need to find the change in total cost when the quantity of shoe inserts increases by one pair.
From the table you provided:
To find the marginal cost for the first pair, there's no previous quantity, so the marginal cost for the first pair is the same as the total cost for the first pair, which is $7.
To find the marginal cost for the third pair, you subtract the total cost for two pairs from the total cost for three pairs:
Marginal cost for the third pair = Total cost for 3 pairs - Total cost for 2 pairs
Marginal cost for the third pair = $10 - $9
Marginal cost for the third pair = $1
To find the marginal cost for the fifth pair, you subtract the total cost for four pairs from the total cost for five pairs:
Marginal cost for the fifth pair = Total cost for 5 pairs - Total cost for 4 pairs
Marginal cost for the fifth pair = $13 - $11
Marginal cost for the fifth pair = $2
So, the marginal costs are:
The first pair: $7
The third pair: $1
The fifth pair: $2