jmc

Rationalizing each of the two fractions on its own will make creating a common denominator easier. For the first fraction, if we recognize the denominator $\sqrt[5]{16}$ as $\sqrt[5]{2^4}$, then that means multiplying the numerator and denominator by $\sqrt[5]{2}$ will leave us with 2 in the denominator: $$\frac{3}{\sqrt[5]{16}}\cdot \frac{\sqrt[5]{2}}{\sqrt[5]{2}}=\frac{3\sqrt[5]{2}}{\sqrt[5]{2^5}}=\frac{3\sqrt[5]{2}}{2}.$$For the second fraction, we have $\frac{1}{\sqrt{3}}\cdot \frac{\sqrt{3}}{\sqrt{3}}=\frac{\sqrt{3}}{3}$. Now we find a common denominator: $$\frac{3\sqrt[5]{2}}{2}+\frac{\sqrt{3}}{3}=\frac{9\sqrt[5]{2}+2\sqrt{3}}{6}.$$So, matching our answer with the form in the problem, we get that $a=3$ and $b=2$, which means $a+b=\boxed{5}$.