To simplify the expression \( \sqrt{28} + \sqrt{28} + \sqrt{28} \), we can start by rewriting it:
\[ \sqrt{28} + \sqrt{28} + \sqrt{28} = 3\sqrt{28} \]
Next, we can simplify \( \sqrt{28} \):
\[ \sqrt{28} = \sqrt{4 \times 7} = \sqrt{4} \cdot \sqrt{7} = 2\sqrt{7} \]
Now we can substitute \( \sqrt{28} \) back into the expression:
\[ 3\sqrt{28} = 3 \times 2\sqrt{7} = 6\sqrt{7} \]
Thus, the simplified expression \( \sqrt{28} + \sqrt{28} + \sqrt{28} \) is:
\[ \boxed{6\sqrt{7}} \]