The slope of Ax + By = 3 is -A/B
And x + 3y = - 5 ⇒ 3y = -x - 5 divide through by 3 ⇒ y = (-1/3) - 5/3
So....the slope of the second line = (-1/3)
And since this is parallel to the first line, this implies that
-1/3 = -A/B
So A = 1 and B = 3
Then B - A = 3 - 1 = 2
