Goal: Get a single x alone, equal to a number — that's your answer.
Add to each side: Use the + / − buttons to choose how many tiles, then drag onto a reactor — or just tap the tile then tap a reactor. The sign in the middle turns into > or < to show it's unbalanced — add the same tiles to the other reactor to bring it back to =.
Zero pairs: A tile and its opposite (like −4 added to +4) cancel and vanish in smoke.
Positive / negative: A positive count is a normal tile. A negative count (press − below zero) turns it red — that removes / cools.
Multiply or divide: Pick × or ÷, choose a value, then press Apply to both cores.