Sol. $$ \begin{aligned} & \frac{\Delta Q}{\Delta t}=-K\left(T-T_0\right) \\ & \frac{\Delta Q}{\Delta t}=-K\left(T_{a v q}-T_0\right) \\ & \text { (i) } \frac{\mathrm{ms} \times 12}{2}=-\mathrm{K}\left(\frac{98+86}{2}-22\right) \\ & 6=-\frac{\mathrm{K}}{\mathrm{~ms}}\left[\frac{98+66}{2}-22\right] \\ & 6=-\frac{\mathrm{K}}{\mathrm{~ms}}[70] \end{aligned} $$ (ii) $$ \begin{aligned} & \frac{\mathrm{ms} \times 6}{\Delta \mathrm{t}}=-\kappa\left(\frac{75+69}{2}-22\right) \\ & \frac{6}{\Delta \mathrm{t}}=-\frac{\mathrm{K}}{\mathrm{~ms}}(50) \end{aligned} $$ (ii) ÷ (i) $$ \begin{aligned} & \frac{6}{\Delta \mathrm{t}(6)}=\frac{50}{70} \\ & \Delta \mathrm{t}=\frac{7}{5}=1.4 \mathrm{~min} \end{aligned} $$