Can someone show me the easiest way to do this WACC problem on a TI-84 calculator?

10) A firm has determined its cost of each source of capital and its optimal capital structure, which is shown in the table below. Using this table, the firm's weighted average cost of capital (WACC) is calculated as Source of Capital Long-term debt Preferred stock Common stock equity Target Market Proportions 40% 10 50 After-Tax Cost 6 11 15 A) 6.00% B) 7.70% 0 9.50% 11.00%