What is 12c - c in simplest form?

Imagine that the variable c represents something tangible, like an orange.  So what this equation is asking is subtract 1 orange from 12 oranges.  So you are left with 11 oranges.

Another way to think about this problem is if you rewrite the equation slightly to:
 
12c - c =
12c - 1c = 
11c

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