The rate of change is also known as the slope. In order to find the slope, we can put this equation into slope-intercept form, or y = mx + b.
3x - 4y = 6
3x = 4y + 6
3x - 6 = 4y
y = (3/4)x - 3/2
The rate of change, or slope, is 3/4.
Hope this helps!! :)