$$ \begin{matrix} H.& Min.& Sec. \\ 31 & 26 & 25 \\ \dot{1} \dot{8} & \dot{5} \dot{8} & 57 \end{matrix} \\ \_\_\_\_\_\_\_\_\_\_\_\_\_\_ \\ 12 \quad \quad 27 \quad \quad 28 \quad \\ \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_$$
$$ \therefore $$ 12 hr 27 m 28 sec.
Steps
1. Measurement unit in 'time' column-wise base is different
2. In column of minute and second there will be two base.
(a) Base in unit column of both $$ = 10 $$
(b) Base in time column of both $$ = 6$$
3. Base in column of hour $$ = 10$$
4. The base of getting complement digits in the tens columns of minute and second $$= 6$$ and in remaining base $$ = 10$$
Remark : general base considered in decimal.