Combine like terms: group the \(a\) terms and the constants separately.<br><br>
&bull; Like terms with \(a\): \(a + 2a = 3a\)<br>
&bull; Constants: \(4 + 1 = 5\)<br>
&bull; Result: \(3a + 5\)<br><br>
Final Answer: C: \(3a + 5\)