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0.5a+0.9(13-a)=8.9
We move all terms to the left:
0.5a+0.9(13-a)-(8.9)=0
We add all the numbers together, and all the variables
0.5a+0.9(-1a+13)-(8.9)=0
We add all the numbers together, and all the variables
0.5a+0.9(-1a+13)-8.9=0
We multiply parentheses
0.5a-0.9a+11.7-8.9=0
We add all the numbers together, and all the variables
-0.4a+2.8=0
We move all terms containing a to the left, all other terms to the right
-0.4a=-2.8
a=-2.8/-0.4
a=6+0.4/0.4
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