Leap Inc. is all$-$equity and has two business divisions: a battery manufacturing division and a solar panel installation

division. $80\%$ of Leap's revenue comes from the battery manufacturing division and $20\%$ comes from the solar panel

installation division. The battery manufacturing division has a cost of capital of $4\%,$ while the solar panel installation

division has a cost of capital of $10\%.$ Leap is considering the acquisition of another battery manufacturer and has

begun forecasting cash flows for that business. What is the appropriate cost of capital to discount the future cash flows

of that business?

The appropriate cost of capital is closest to: