Algebra 1: Common Core (15th Edition)

$x=-4$
When you model the equation using algebra tiles, you get 1 green tile, 1 yellow tile, the black bar, and 3 red tiles. The green tile represents x. To isolate x or the green tile by itself on one side of the equation or the black bar, subtract the number of yellow tiles from the red tiles on the other side. You do this to cancel out the $+1$, so you subtract $-1$ from both sides, which leaves you with $x=-4$. One green tile and $4$ red tiles.