Homework help?!?!?

I have to make a time line on ancient Egypt, and every website I've been to says different dates and I'm so confused! When did Cleopatra come to power? When did Alexander the Great liberate Egypt? These stupid websites say Cleo came to power in 51 BC and Alexander conquered in 332 BC, which doesnt make sense, because that would mean that Cleo came to power almost 150 years AFTER Alex conquered? I'M SO CONFUSED PLEASE HELP ME!!!