A car moving on a straight road with constant velocity \( 72 \,\text{km/hr} \) sees an old lady crossing the road at \( 42 \,\text{m} \) ahead of the car. If reaction time (time lag between information received and action taken) of car driver is \( 0.1 \,\text{sec} \), find minimum retardation (in \( \text{m/s}^{2} \)) of car so as to avoid accident.
