Slope-intercept form is y=mx+b, so 1st thing you have to do is isolate the y variable. To do that, you would subtract 9x from both sides:
9x+2y=3
-9x -9x
2y=3-9x
We have y on one side, but the 2 is still in front of it. So now you have to divide the whole equation by 2
2y=3-9x y=mx+b
— —— ➡️y=(3/2)-(9/2)x
2 2
Since we now have the b and mx mixed up, all you have to do is switch them
y=(3/2)-(9/2)x
↖️↗️
y=-9/2x+3/2