Giovanna,
218 is right to get the first light to come on. Now you have to start again. Once that light is on, go back to
= and see what number is beside it this time. Then subtract the new number beside A from that, and keep going just like you did before.
If that's not clear enough, I can play through the game again and maybe get an answer to you with numbers tonight. Unfortunately, my saves for this game never work when I reinstall it, so it will take me a while.
Let me know.

Gil.