Answer :

Sure, let's solve this step-by-step.

1. Identify the largest 4-digit number:
The largest 4-digit number is 9999.

2. Identify the target number:
The target number given in the question is 67,890.

3. Find out how much to add to the largest 4-digit number to reach the target number:
To do this, subtract the largest 4-digit number from the target number.

Let's outline it mathematically:
[tex]\[ \text{Value to add} = \text{Target number} - \text{Largest 4-digit number} \][/tex]
Substitute the numerical values:
[tex]\[ \text{Value to add} = 67,890 - 9999 \][/tex]

4. Compute the result:
We find that:
[tex]\[ 67,890 - 9999 = 57,891 \][/tex]

So, you need to add 57,891 to the largest 4-digit number, 9999, to get 67,890. The final answer is 57,891.