please go over step by step with the formula on paper please

Debt Preferred Common equity 0.45 0.35 0.20 The firm's debt is in the form of bonds with a 5.3% coupon rate and a 6.4% market or yield rate. The bonds have a thirty year term. The firm's combined tax rate is 36%. The cost of preferred shares is 8%, and the cost of common equity in the form of retained earnings is 15%. The cost of issuing new common is 18%. 4 a) Assuming the firm's common equity consists of retained earnings, find the weighted average cost of capital (WACC). 2 b) The firm has $1,200,000 in retained earnings. Find the breakpoint or size of total investment in dollars at which the firm will run out of retained earnings and have to issue new common. 2) Find the marginal cost of capital after the firm has run out of retained earnings and issued new common