You are given that
$$S = 4 + \frac { 8 k } { 7 } + \frac { 16 k ^ { 2 } } { 49 } + \frac { 32 k ^ { 3 } } { 343 } + \cdots + 4 \left( \frac { 2 k } { 7 } \right) ^ { n } + \cdots$$
The value for $k$ is chosen as an integer in the range $- 5 \leq k \leq 5$
All possible values for $k$ are equally likely to be chosen.
What is the probability that the value of $S$ is a finite number greater than 3 ?