Equations have to be in the form a+(b+c)+d. One of the variables must be x, for the target. The variables can be anything, and the + can be any operator that is +, -, *, /, or ^. Also, I'm pretty sure the game acts like the equation is actually x+(x+x+x), but that's just from experience. If you need more complex math, like you're doing here, you can use helper simulations that are hidden, i.e. due a bit of math in a hidden simulation, then use that in the simulation. It might have to be at the end if you refer to another simulation, I'm not sure.