Find the value of B - A

Line 1 = $x + 3y = -5$

Line 2 = $Ax + By = 3$

Rearrange Line 1 into slope intercept form,

Line 1 = $y = -x/3 - 5$

Because Line 2 has the same slope,

Line 2 = $y = -x/3 + b$

Multiply Line 2 by 3 on both sides and convert to standard form,

Line 2 = $3y = -x + 3b$

Line 2 = $x + 3y = 3b$

Line 2 must pass through (-7, 2), so we can plug in these values,

Line 2 = $-1 = 3b$

$b = -1/3$

Line 2 = $x + 3y = -1$

Multiply both sides by -3,

Line 2 = $-3x + -9y = 3$

B - A = -9 - (-3) = -6