Three Hundred
numeral
You have three hundreds. What does that come out to? Three hundred.
さんびゃく
The reading is a little bit weird, so be careful. You should already know the on'yomi readings, but the ひゃく rendakus to びゃく. This pattern will repeat itself with 三 + many counter kanjis that can rendaku, so pay attention for it as you read Japanese.
まんがを三百さつもっています。
I have three hundred manga.
ひるねをしていた時に、だれかがインターホンを三百回もならした。
When I was taking a nap, somebody rang the doorbell 300 times.
一年は三百六十五日です。
One year is three hundred and sixty-five days.