I’m not sure what happened while you were writing this, but if I’m reading it right, “My” has 18 books. If “My” has 3 times as many as 6, that also means 3 times 6, which is 18.
The answer c, because they got 9 out of 15 flips being heads. This probability is 0.6. The other answers are not accurate.
It's not compounded interest, you just get $3.20 every year.
$100 * 0.032 = $3.20
$3.20 * 3 years = $9.60