A clock hung on a wall has marks instead of numerals in its dial. On the adjoining wall, there is a plane mirror and the image of the clock in the minor indicates the time 4.20. Then the time on the clock is

In a plane mirror, the image undergoes depth inversion. So, the time in the image clock is as much ahead of 12 hours zero minute as the time on the actual clock is behind 12 hours zero minute. So, time one actual clock is 12h ▬ 4h 20 min : 7 h 40 min.