A firm has determined its cost of each source of capital and optimal capital structure, which is composed of the following sources and current market value proportions:

$\backslash$table$[[$Source of Capital,$\backslash$table$[[$Market$],[$Proportions$]],\backslash$table$[[$After$-$Tax$],[$Cost$]]],[$Long$-$term debt,$45\%,5\%$