If you don't do as well here as you've done with the earlier stages, spend some more time with these. It's worth it. Don't move on until these are fast and easy. If you think you know them, go back to the fives, then come back to these and see if you do these as quickly. If not, practice them some more and try it again.
Numbers multiplied by four are always even.
So, if you double something, then double it again, you're multiplying by four.