If $$ \displaystyle C_{r}=^{n}C_{r} $$ then to evaluate the expansion $$ \displaystyle A=\sum \sum_{0\leq r\leq s\leq n}^{} $$ $$ \displaystyle C_{r}C_{s} $$, We make use of $$ \displaystyle \sum_{r=0}^{n}C_{r}^{2}=^{2n}C_{n} $$ and the expansion of $$ \displaystyle \left ( \sum_{r=0}^{n}C_{r} \right )^{2} $$. On the basis of above information answer the following questions.

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