Table $10\mathrm{.}3\mathrm{.}1$

$\backslash$table$[[\backslash$table$[[$Labour$],[($workers per$],[$day$)]],\backslash$table$[[$Output$],[($teapots per $($dollars per$($dollars per$($dollars per$],[$day$)]],$day$),$day$),$day$)],[0,0,20,0,20],[1,4,20,-,45],[2,9,20,--,70],[3,13,20,--,95],[4,16,20,100,-],[5,18,20,125,145]]$

Refer to Table $10\mathrm{.}3\mathrm{.}1,$ which gives Tania's Teapots' total cost schedule. When output increases from $4$ to $9$ teapots, the marginal cost of one of the $5$ teapots is

a$.$ $$6\mathrm{.}25.$

b$.$ $$25.$

c$.$ $$5.$

d$.$ $$4\mathrm{.}25.$

e$.$ $$4.$