- 5 = 11

Add "+ 5" to both sides to get rid of the "- 5" on the left:

 - 5 = 11
  + 5  + 5
------------------
     = 16

Multiply both sides by 2 to get rid of the denominator 2 on the left:

  2· = 2·16

The 2's cancel on the left leaving just "c".  2·16 on the right gives 32

    c = 32

Edwin