Answers

2014-09-24T17:29:57+08:00
That's simple 
the sum of a,b,c is basically saying : a+b+c that it , that's the answer. unless the variable  has a corresponding number for example:
if a=2,b=3.c=1
a+b+c=6  
2+3+1=6
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2014-09-26T13:57:11+08:00
Just simply add the three variables. Since you cannot add different variables, Just like you can't add those with have different units, just leave it as a+b+c. That's it.

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