1. The problem asks to simplify the expression $-(-18)$. 2. The expression has a negative sign outside the parentheses and another negative sign inside. 3. According to the rule of double negatives, $-(-a) = a$. This means the two negatives cancel each other out. 4. Applying this rule, $-(-18) = 18$. 5. Therefore, the simplified value is $18$.