Find A and B so the graph of Ax+By=-4 has the points (-8,4) and (-3,1)

I haven't a clue how to solve this.
A.) A=8, B=4
B.) A=-3, B=-5
C.) A=4, B=8
D.) A=3, B=5

Substitute the points' x and y values into the equation:

A(-8) + B(4) = -4
A(-3) + B(1) = -4

Rewrite into more conventional form:

-8A + 4B = -4
-3A + B = -4

Multiply through equation 2 by 4 to get the B coefficients to match:

-12A + 4B = -16

Subtract that from equation 1:

-8A + 4B = -4
-(-12A + 4B = -16)
-----------------------
4A = 12

Divide both sides by 4:

A = 3

Substitute 3 for A in either original equation to solve for B,