Question 169066
12a-5b=18
15a-5b=30
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Using the "elimination method", multiply the top equation by -1 and then combine both equations:
-12a+5b=-18
 15a-5b= 30
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  3a   = 12
   a   = 4
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Using the above, substitute it back into either equation (I'll use the first one) and solve for 'b':
12a-5b=18
12(4)-5b=18
48-5b=18
-5b=-30
  b= 6
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Solution:
a = 4
b = 6