$q(t)=en(t)\Rightarrow \overline{I}=\frac{\Delta q}{\Delta t}=e\times \frac{\Delta n}{\Delta t}$ $\Rightarrow \overline{I}=e\times \frac{{{n}_{2}}-{{n}_{1}}}{{{t}_{2}}-{{t}_{1}}}=e\times \frac{(58{{t}_{2}}+27)-(58{{t}_{1}}+27)}{{{t}_{2}}-{{t}_{1}}}$ $\Rightarrow \overline{I}=e\times \frac{58({{t}_{2}}-{{t}_{1}})}{{{t}_{2}}-{{t}_{1}}}=(e\times 58)A$ $\xrightarrow{e=1/6\times {{10}^{-19}}C}\overline{I}=1/6\times {{10}^{-19}}\times 58=9/28\times {{10}^{-18}}A$ $\Rightarrow \overline{I}=9/28\times {{10}^{-15}}mA$