Refer to Table $12\mathrm{.}2\mathrm{.}1,$ which gives the total revenue schedule and total cost schedule of a perfectly competitive firm. Economic profit is maximized when the firm produces $q,$ units of output.

Table $12\mathrm{.}2\mathrm{.}1$

$\backslash$table$[[\backslash$table$[[$Output$],[($units$)]],\backslash$table$[[$Total Revenue Total Cost$],[($dollars$)]],\backslash$table$[[($dollars$)],[0]]],[0,0,25],[1,30,49],[2,60,69],[3,90,86],[4,120,100],[5,150,116],[6,180,136],[7,210,176]]$

a$.3$

b$.5$

c$.$ zero

d$.6$

e$.7$