There are 7 yellow balls, 4 green balls, 3 red balls and 6 blue balls. If a ball is selected at random what is the probability that it i not a blue ball?

Question

$\begin{array}{11} (a)\; \frac{6}{20} \\ (b)\; \frac{7}{20} \\ (c)\; \frac{14}{20} \\ (d)\; \frac{4}{20} \end{array}$