For a gene A, a geneticist studying a population of butterflies found the following genotypes: $\begin{array}{c}\begin{array}{r}108 \\144 \\48\end{array} \begin{array}{lll} \text {\( A A \) butterflies }\\ \text {Aa butterflies }\\ \text { aa butterflies}\end{array}\end{array}$

-What is the frequency of the a allele in the butterfly population?