What is the solution to the open sentence 18 = c + 6?

This is very simple, all you have to do is subtract 18 and 6 and that would be 12, and now we have 12 as a POSSIBLE answer, lets check our work to be 100% correct so now try to add 12 and 6 and we get 18, so yay it made the equation true and since its true its right so that's the answer.

c = 12 so 18 = 12 + 6 is true.

Subtract 6 from both side wich will leaveyou with a answer of 12=c

Iam unsure about what the proof is, therefore as much as wish to i can not.