Question 131201
X) a-b=7
Y) a-4b=-7
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X) a=b+7
Y) 
(b+7)-4b=-7
b+7-4b=-7
-3b=-14
b=14/3
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X) 
a- 14/3=-7
3a-14=21
3a=35
a=35/3
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Ed