total variable cost divided by total output.

the change in total cost from producing one more unit of output.

total cost divided by total output.

the change in fived cost from producing one more unit of output.

From the information given in the table, calculate the marginal cost of the $3$ rd unit of output.

$\backslash$table$[[$Output $($units$),$Total cost $($$$),$Marginal cost $($$$)],[0,20,$N$/$A$],[1,35,15],[2,45,10],[3,65,],[4,90,25]]$