1. The problem is to evaluate the expression $(-18) + 12$. 2. This is a simple addition problem involving integers, where you add a negative number and a positive number. 3. The rule for adding integers with different signs is to subtract the smaller absolute value from the larger absolute value and take the sign of the number with the larger absolute value. 4. Calculate the absolute values: $|{-18}| = 18$ and $|12| = 12$. 5. Subtract the smaller absolute value from the larger: $18 - 12 = 6$. 6. Since $-18$ has the larger absolute value and is negative, the result is $-6$. 7. Therefore, $(-18) + 12 = -6$.