You multiply the -3 into the (2-x). which gives you -6+3x=9x. Know you wanna get ride of the 3x so you subtract from both sides, which then gives you. -6=6x. From here were gonna need to get x by itself so you divide both sides by 6.
The horizontal change is called the run and the vertical is rise. so for example if one point to the other rises by 4 and runs by 5, the slope is 4/5. slope is rise / run