The x intercept is -3 so the point (-3,0) is on the line. This point is on the horizontal x axis. The x intercept is always in the form (NUMBER,0) where you replace "NUMBER" with any number you want.
The y intercept is -4 so we know that (0,-4) is also on the line. This is on the vertical y axis. The y intercept is always in the form (0,NUMBER)
Use the slope formula to find the slope of the line through the points (-3,0) and (0,-4)
m = (y2-y1)/(x2-x1)
m = (-4-0)/(0-(-3))
m = (-4-0)/(0+3)
m = -4/3
The answer is choice B: -4/3
I have a feeling you mixed up x and y somehow when you got -3/4