Add the following integers :
0 and `-21`

Answer

To solve the problem of adding the integers 0 and -21, we can follow these steps:

### Step 1: Write down the expression
We start with the expression:
\[ 0 + (-21) \]

### Step 2: Understand the operation
Here, we are adding 0 and -21. We know that adding 0 to any number does not change the value of that number.

### Step 3: Apply the addition rule
According to the rules of addition:
\[ 0 + (-21) = -21 \]

### Step 4: Conclude the result
Thus, the result of adding 0 and -21 is:
\[ -21 \]

### Final Answer:
The sum of 0 and -21 is:
\[ -21 \]

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