To perform the operation \( 3 \sqrt{5} \times 7 \sqrt{11} \), we can follow these steps:
- Multiply the coefficients (the numbers outside the square roots).
- Multiply the square roots together.
So we have:
\[ 3 \sqrt{5} \times 7 \sqrt{11} = (3 \times 7) \times (\sqrt{5} \times \sqrt{11}) \]
Calculating the coefficients:
\[ 3 \times 7 = 21 \]
Now for the square roots:
\[ \sqrt{5} \times \sqrt{11} = \sqrt{5 \times 11} = \sqrt{55} \]
Putting it all together:
\[ 3 \sqrt{5} \times 7 \sqrt{11} = 21 \sqrt{55} \]
Thus, the exact answer (in its simplest form) is:
\[ \boxed{21 \sqrt{55}} \]