Question 727117
a-4b=11 multiply by -5 & ad.
5a-7b=-10 
-5a+20b=-55
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13b=-65
b=-65/13
b=-5 ans.
a-4(-5)=11
a+20=11
a=11-20
a=-9 ans.
Proof:
5(-9)-7(-5)=-10
-45+35=-10
-10=-10