Helpful Hardware sells windows $(80\%$ of sales$)$ and doors $(20\%$ of sales$).$ The selling price of

each window is $$400$ and of each door is $$1,000.$ The variable cost of each window is $$250$

and of each door is $$700.$ Fixed costs are $$1,440,000.$ The break$-$even point in units using

the weighted$-$average contribution margin is:

a$.3,200$ units.

b$.8,000$ units.

c$.12,000$ units.

d$.6,858$ units.

e$.5,334$ units.