the correct answer is $7\%,$ but I don't know why

ABC Inc., a U$.$S$.$ company, is considering changing its capital structure. The company has debt and equity in its capital structure and the current D$/$E ratio is $0\mathrm{.}4,$ the current weighted average cost of capital of ABC is $10\mathrm{.}69\%$ p$.$a$.$ The current before$-$tax cost of debt capital for ABC is $10\%$ p$.$a$.,$ the current cost of equity is $12\mathrm{.}17\%$ and current equity beta is $1\mathrm{.}024.$ The risk$-$free rate and market risk premium are $5\%$ and $7\%$ p$.$a$.$ respectively. The corporate tax rate is $30\%.$ If the company switches to a capital structure with $100\%$ equity, which of the following is closest to the new weighted average cost of capital of ABC Inc $($using the approach covered in the lecture$)?$

Not able to answer, need more information.

$12\mathrm{.}17\%$ p$.$a$.$

$7\mathrm{.}42\%$ p$.$a$.$

$10\mathrm{.}60\%$ p$.$a$.$

$7\mathrm{.}00\%$ p$.$a$.$