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5.16-12a-13a=-9
We move all terms to the left:
5.16-12a-13a-(-9)=0
We add all the numbers together, and all the variables
-25a+14.16=0
We move all terms containing a to the left, all other terms to the right
-25a=-14.16
a=-14.16/-25
a=12.206896551724/21.551724137931
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