Plank$$s Plants had net income of $$2,000$ on sales of $$50,000$ last year. The firm paid a dividend of $$500.$ Total assets were $$100,000,$ of which $$40,000$ was financed by debt.

$($a$)$ What is the firm$$s sustainable growth rate? Express your answer as a percentage.

$($b$)$ If the firm grows at its sustainable growth rate, how much debt will be issued next year?