Add the rational expressions.
\[
\frac{18 a-1}{3 a+3}+\frac{13-6 a}{3 a+3}
\]
The simplified sum of the rational expressions is \(\boxed{4}\)
Step 1 :Combine the numerators: \(18a-1+13-6a\)
Step 2 :Simplify the numerator: \(12a+12\)
Step 3 :Factor out the common factor in the numerator and denominator: \(\frac{12(a+1)}{3(a+1)}\)
Step 4 :Cancel out the common factor: \(\frac{12}{3} = 4\)
Step 5 :The simplified sum of the rational expressions is \(\boxed{4}\)