Given:
- Cost price of 20 tables = Rs. 12,000.
- CP of 1 table:
\[
\text{CP of 1 table} = \frac{12000}{20} = 600
\]
- Total profit = Selling price of 4 tables.
- Let SP of 1 table be Rs. x.
Total SP:
\[
\text{Total SP} = \text{Total CP} + \text{Profit}
\]
\[
= 12000 + 4x
\]
Since 20 tables were sold:
\[
20x = 12000 + 4x
\]
Solving for \( x \):
\[
20x - 4x = 12000
\]
\[
16x = 12000
\]
\[
x = \frac{12000}{16} = 750
\]
Thus, the correct answer is Rs. 750.