First, we must put the equation you gave into slop-intercept form, where it will be easy to see the slope. We do this through algebra:
4x-3y=-7
4x=-17+3y (add 3y to both sides)
4x +17 = 3y (add 17 to both sides)
4/3x + 17/3 = y (divide both sides by 3)
Now, we have the equation y=4/3x+17/3. Knowing that in this form y=mx+b, m is the slope. This means that the slope of this line is 4/3.
To find a perpendicular line, we know that it's slope will be the negative reciprocal. So, the slope of our new line is -3/4.
Now, we can plug this new slope, along with the given point (-8,-4) into our y=mx+b equation and solve for b, our y-intercept.
y=mx+b
-4=-3/4(-8)+b
-4=6+b (multiply -3/4 and -8)
-10=b (subtract 6 from both sides)
Here we found that the y-intercept of our perpendicular line is -10. Now we have all the pieces we need to write the equation of our new line in slope-intercept form:
y=-3/4x-10
We can check our work by plugging in the x-coordinate -8 and seeing if we get the correct y-coordinate of -4:
y=-3/4(-8)-10
y=6-10
y=-4
Therefore, the answer we found is correct.