Texas Transport has five possible investment projects for the coming year. Each project is indivisible. They are:

Project Investment (million IRR

A $ 6 18%

B $10 15%

C $9 20%

D $4 12%

E $3 24%

The firm's weighted marginal cost of capital schedule is 12 percent for up to $6 million of investment; 16 percent for between $6 million and $18 million of investment; and above $18 million the weighted cost of capital is 18 percent. The optimal capital budget is:

$12 million.

$18 million.

$23 million.

$28 million.