Благой вечер Помогите пожалуйста.Find the mistakes and write down the correct

Добрый вечер Помогите пожалуйста.
Find the mistakes and write down the correct sentences.
1.European explorers crossed the atlantic ocean before the 15th century.
2. They knew a lot about the atlantic ocean.
3. Columbus saw america for the first time on the 10th of october, 1492.
4. It took him 5 months to cross the atlantic ocean.
5.They had very fast ships.
6.We celebrate columbus day on the 14th october.