YOU SAID:

I went to the store and killed thirty eight million hippos

INTO JAPANESE

私は店に行って3800万頭のカバを殺した

BACK INTO ENGLISH

I went to the store and killed 38 million hippos.

INTO JAPANESE

私は店に行って、3800万頭のカバを殺しました。

BACK INTO ENGLISH

I went to the store and killed 38 million hippos.