Donald opens a margin account and purchases $2000$ shares of $3609.$HKU at $$30$ per share. He borrows $$15,000$ from his broker to help pay for the purchase. The annual interest rate on the loan is $8\%.$

$($a$)$ What is the break$-$even stock price after one year?

$($b$)$ If the share price rises to $$35$ per share by the end of the year, what is the rate of return on the investment?

$($c$)$ If the share price falls to $$25$ per share by the end of the year, what is the rate of return on the investment?

$($d$)$ i$.$ Repeat parts $($a$)$ to $($c$)$ if Donald invests without borrowing.

ii$.$ From the above results, what can you comment on investing on margin?