The correct answer is 11.

Please Note:
Use inverse operations to solve the equation for a variable.

Solution:
To solve the given equation for variable c, we use inverse operations.

Given equation:
c + 7 = 18

Now, subtract 7 from both sides and simplify.

c + 7 – 7 =  18 - 7

⇒        c   =   11

So, the value of c is 11.