Let $๐={๐ค_1,๐ค_2,โฆโฆ.}$ be the sample space associated to a random experiment. Let $๐(๐ค_๐)= \frac{๐(๐ค_{๐โ1})}{2} ,๐โฅ2.$ Let ๐ด=${(2๐+3๐:k,๐โโ)}$ and $๐ต={๐ค_๐:๐โ๐ด}$. Then ๐( ๐ต) is equal to