A bag contains six balls of different colours. Two balls are drawn in succession with replacement. The probability that both the balls are of the…

A bag contains six balls of different colours. Two balls are drawn in succession with replacement. The probability that both the balls are of the same colour is $\displaystyle p$. Next four balls are drawn in succession with replacement and the probability that exactly three balls are of the same colour is $\displaystyle q$. If $\displaystyle p: q=m: n$, where $\displaystyle m$ and $\displaystyle n$ are coprime, then $\displaystyle m+n$ is equal to $\displaystyle \_\_\_\_$.