y = mx + b
8x - 4y - 9 = 0
first you move the nine to the other side of the equal sign (add nine to both sides)
8x - 4y = 9
then you need to also move your 8x over to the other side as well (remember we are trying to get y by itself!)
- 4y = -8x + 9
then we are going to divide -4 to both sides
and you get
y = 2x - 9/4
we can then identify the slope as 2
so B. 2 would be your answer
hope this helped