Step 1: Simplify each square root.
\[
\sqrt{27} = \sqrt{9 \times 3} = 3\sqrt{3}, \quad \sqrt{18} = \sqrt{9 \times 2} = 3\sqrt{2}, \quad \sqrt{147} = \sqrt{49 \times 3} = 7\sqrt{3}.
\]
Step 2: Substitute and simplify.
Now substitute the simplified square roots into the original expression:
\[
3\sqrt{27} + 5\sqrt{18} - 3\sqrt{147} = 3(3\sqrt{3}) + 5(3\sqrt{2}) - 3(7\sqrt{3}) = 9\sqrt{3} + 15\sqrt{2} - 21\sqrt{3}.
\]
Step 3: Combine like terms.
\[
9\sqrt{3} - 21\sqrt{3} = -12\sqrt{3}, \quad 15\sqrt{2} \, \text{remains unchanged}.
\]
Thus, the simplified expression is:
\[
-12\sqrt{3} + 15\sqrt{2}.
\]
Step 4: Conclusion.
Thus, the final answer is \( 8\sqrt{3} \).