Afirm has determined its cost of each source of capital and its optimal capital structure which is comprised of the following sources;
long-term debt = 45%, after-tax cost = 7%
preferred stock = 15%, after-tax cost = 10%
common stock equity = 40%, after-tax cost = 14%
the weighted average cost of capital for this firm is;

10.25%

Explanation:

Data provided in the question:

Long-term debt = 45%, after-tax cost = 7%

Preferred stock = 15%, after-tax cost = 10%

Common stock equity = 40%, after-tax cost = 14%

Now,

The  weighted average cost of capital for this firm will be calculated as:

= Long term debt × after-tax cost + Preferred stock × after-tax cost + Common stock equity × after-tax cost

or

= 0.45 × 0.07 + 0.15 × 0.10 + 0.40 × 0.14

or

= 0.0315 + 0.015 + 0.056

= 0.1025

or

= 0.1025 × 100%

= 10.25%