a$)$ Suppose we use a triangular matrix to count pairs and the number of items n $=20.$ If we store this triangular matrix as a ragged one$-$dimensional array Count, what is the index where count of pair $(7,8)$ is stored? $(3$ points$)$ b$)$ Suppose you are provided with the prior knowledge that only ten percent of the total tabular method should be preferred and why? $(3$ points$)$