5a -3b+a+3b

To simplify the expression \(5a - 3b + a + 3b\), you can combine like terms.

1. Combine the \(a\) terms: \[ 5a + a = 6a \]

2. Combine the \(b\) terms: \[ -3b + 3b = 0 \]

Putting it all together, you get: \[ 6a + 0 = 6a \]

So, the simplified expression is: \[ \boxed{6a} \]