Based on the information below, what is Cali Enterprises optimal capital structure?

Debt = 80%, Equity = 20%, EPS = $3.42; Stock Price = $30.00

Debt = 60%, Equity = 40%, EPS = $3.18; Stock Price = $31.20

Debt = 50%, Equity = 50%, EPS = $3.05; Stock Price = $28.90

Debt = 40%, Equity = 60%, EPS = $2.95; Stock Price = $26.50

Debt = 70%, Equity = 30%, EPS = $3.31; Stock Price = $30.40

If possible, please explain why.