since (2,1) lies on it
2A + B = 7 or B = 7 - 2a
slope of 2x-7=3 is 2/7
slope of Ax + By = 7 is -A/B
so -A/B = 2/7
2B = -7A
2(7-2A) = -7A
14 - 4A = -7A
3A = -14
A = -14/3
B = 7-2(-14/3) = 49/3
B - A = 49/3 - (-14/3) = 21
Find B - A if the graph of Ax + By = 7 passes through (2,1) and is parallel to the graph of 2x - 7y = 3.
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