for slope, the equation is y = mx + b, and so you must reorder them to fit the equation
first move the x over
2x (-2x) + 3y = 6 (-2x)
your equation will look like this now:
3y = -2x + 6
as the form is y = mx + b, you must isolate the y by dividing the 3 to both sides.
3y/3 = (-2x + 6)/3
y = -2x/3 + 2
your equation is
y = -2/3x + 2
your slope is m, which is -2/3 in this case
your answer is -2/3
hope this helps