2.10.130 Number Series

Condition: using the determination of the convergence of the series, prove the convergence of the row and find its amount. a) \ (\ sum_ {n = 0}^{\ infty} \ frac {1} {(n+7) (n+9)} \); b) \ (\ sum_ {n = 1}^{\ infty} \ frac {5^{n+1} -7 \ cdot 3^{n}} {10^{n}} \).