An analyst gathered the following data about a company:
| Capial Srucure | Required Rate of Return |
| 30 percent debt | 10 percent for debt |
| 20 percent preferred stock | 11 percent for preferred sock |
| 50 percent common stock | 18 percent for common stock |
Assuming a 40 percent tax rate, what after-tax rate of return must the company earn on its investments?（ ）
0.3×0.1×(1-0.4)+0.2×0.11+0.5×0.18=0.13.