Note that the slope-intercept form is: y = mx + b
First, set the equation as such
2x (-2x) + 3y = (- 2x) + 15
3y = -2x + 15
Isolate the y. Divide 3 from both sides
(3y)/3 = (-2x + 15)/3
y = (-2/3)x + 5
-2/3 is your slope
hope this helps
