Answer:
Let’s call missing number x:
1. Replace x with missing number:
X + (-11) + 111 = 130
2. Simplify
X - 11 + 111 = 130
X + 111 - 11 = 130
X + 100 = 130
3. Make 110 to the right side, without forgetting to change the sign:
X = 130 - 100
X = 30
So x (missing number) is equal to 20. Hope this helps!