So you are given y-4 = 5/4(x+3). This is from a form called point-slope form, written as y-y1 = m(x-x1). This gives us the slope. From looking at our original equation we see m = 5/4. To find it perpendicular, we do the negative reciprocal meaning we flip the fraction and make it a negative. So we get -4/5. So our slope is -4/5. Now we can use our y = mx + b form and substitute m and our order pair. So we get
8 = (-4/5)(-7) + b
Now we solve for b:
8 = 5.6 + b
b = 2.4
So our equation is:
y = -4/5x + 2.4
