In future you must ask in the Ask the Tutor Forum if you want me to answer. This forum is for students to help each other.
According to Modigliani and Miller, then if there is corporate tax the WACC will be a minimum when borrowings are maximised. (Without corporate tax the WACC will not change). However M&M relies on many assumptions that are unlikely to all hold in practice.
This is all explained in my free lectures on the effect of changes in gearing.