8．
某个体服装店经营各种服装，在某周内获纯利润\(y(\)元\()\)与该周每天销售这种服装件数\(x\)之间的一组数据关系如下表：
\(x\) | \(3\) | \(4\) | \(5\) | \(6\) | \(7\) | \(8\) | \(9\) |
\(y\) | \(66\) | \(69\) | \(73\) | \(81\) | \(89\) | \(90\) | \(91\) |
已知：\(\sum\limits_{i=1}^{7}{x_{i}^{2}}=280\)，\(\sum\limits_{i=1}^{7}{{{x}_{i}}{{y}_{i}}}=3487\)．
\(\begin{cases} & \hat{b}=\dfrac{\sum\limits_{i=1}^{n}{({{x}_{i}}-\overline{x})({{y}_{i}}-\overline{y})}}{\sum\limits_{i=1}^{n}{{{({{x}_{i}}-\overline{x})}^{2}}}}=\dfrac{\sum\limits_{i=1}^{n}{{{x}_{i}}\cdot {{y}_{i}}-n\overline{x}\cdot \overline{y}}}{\sum\limits_{i=1}^{n}{x_{i}^{2}-n{{\overline{x}}^{2}}}} \\ & \hat{a}=\overline{y}-\hat{b}\overline{x} \\ \end{cases}\)
\((\)Ⅰ\()\)求\(\overline{x}\)，\(\overline{y}\)；
\((\)Ⅱ\()\)画出散点图；
\((\)Ⅲ\()\)观察散点图，若\(y\)与\(x\)线性相关，请求纯利润\(y\)与每天销售件数\(x\)之间的回归直线方程．