4. Prove whether or not the following series converge (you do NOT have to find the value they converge to!) \text { (a) } S=\sum_{n=1}^{\infty} a_{n} \text { where }

a_{n}=(-1)^{3 n} \frac{3^{n-1} 2^{n-5}}{5^{n-3}} \text { (b) } S=\sum_{n=1}^{\infty} a_{n} \text { where } a_{n}=\ln (3 n+1)-\ln 2 \pi