The discrete random variable $$\(X\)$$ takes the values $$\(-1,2,3,4\)$$ and 7 only. Given that $$\[ \mathrm{P}(X=x)=\frac{8-x}{k} \text { for } x=-1,2,3,4 \text { and } 7 \]$$ find the value of $$\(\mathrm{E}(X)\)$$ (5)

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