Gaack
"E = c times mass divided by mass and then multiplied by c."
E = c*2 ? You left something out, didn't you?
No. That doesn't work either. Johannes, you have to master algebra before you can tackle relativistic physics.
When you multiply by something, then divide by the same thing, you're right back where you started. Nothing has changed.
Math is like learning to read, to speak a foreign language, or play a musical instrument. You have to be shown how to do it, then practice, practice, practice until you become proficient. It is not imparted by revelation or inspiration. That's what religion is all about: claiming the reward without doing the work.