simplify. Rationalize the denominator.

To simplify the expression \( \frac{3}{7} + 3 \), we first convert the whole number \(3\) into a fraction that has the same denominator as \(\frac{3}{7}\).

We can rewrite \(3\) as \(\frac{3 \times 7}{7} = \frac{21}{7}\).

Now, we can add the two fractions:

\[
\frac{3}{7} + \frac{21}{7} = \frac{3 + 21}{7} = \frac{24}{7}.
\]

So, the simplified form of \( \frac{3}{7} + 3 \) is

\[
\frac{24}{7}.
\]

There is no need to rationalize anything in this case since the denominator is already a simple integer. Thus, the final answer is:

\[
\frac{24}{7}.
\]