The point at which a line goes thru the y axis is called the y-intercept. This point is represented by "b" in the slope-intercept form of a line: y = mx + b
We can "rewrite" your equation into this slope-intercept form using inverse operations and the y-intercept by will be easily identified.
3x - 4y = 12
3x - 4y - 3x = 12 - 3x
-4y = -3x + 12
Divide both sides of the equation by -4:
-4y = ( -3x + 12)
y= 3x - 3
The y-intercept will be -3. The line will intersect the y-axis at (0,-3)
Hope this helps Ariana!