用模型 \(y = a{{\rm{e}}^{kx}}\) 拟合一组数 \(\left( {{x_i},{y_i}} \right)\left( {i = 1,2, \cdot \cdot \cdot ,10} \right)\),若 \({x_1} + {x_2} + \cdots + {x_{10}} = 10\),\({y_1}{y_2} \cdots {y_{10}} = {{\rm{e}}^{70}}\),设 \(z = \ln y\),得变换后的线性回归方程为 \(\widehat z = \widehat bx + 4\),则 \(ak = \)( )