Set it up into the y = mx + b format (slope form)
3x + 2y = 16
3x (-3x) + 2y = (-3x) + 16
2y = -3x + 16
(2y)/2 = (-3x + 16)/2
y = -3/2x + 8
Inside the formula (y = mx + b), m is the slope
-3/2 fits in the m section (next to the x) and so it is the slope
hope this helps