To find the value that fits in the blank, you can divide 10,000 by 20.
So, the calculation is:
\[ 20x = 10,000 \]
Dividing both sides by 20 gives:
\[ x = \frac{10,000}{20} \]
Calculating that, you get:
\[ x = 500 \]
Therefore, the complete equation is:
20x = 10,000, and x = 500.