If $\sum _ { n = 1 } ^ { \infty } c _ { n } x ^ { n }$

Essay

If $\sum _ { n = 1 } ^ { \infty } c _ { n } x ^ { n }$ is convergent at $x = 3$ , what can be said about the convergence or divergence of the following series?
(a) $\sum _ { n = 1 } ^ { \infty } c _ { n } 4 ^ { n }$ (b) $\sum _ { n = 1 } ^ { \infty } c _ { n } ( - 2 ) ^ { n }$ (c) $\sum _ { n = 1 } ^ { \infty } c _ { n } ( - 3 ) ^ { n }$