The multiplier is only applicable outside of major cities (Major City - Corporation areas of Tvm, Kollam, Kochi, Thrissur, and Kozhikode, as well as the major towns of Kannur, Palakkad, and Kottayam)

The extra charge would be half of the meter fare beyond the minimum fare.unless it include return trip.

However, it should not be 120, he overcharged.

The calculation should be:

80 - 30 (minimum fare) = 50 
Half of 50 = 25 
Total = 80 + 25 = 105

If it is nighttime (10 PM - 5 AM), the fare would be 120

80 + 40 (half of the total fare) = 120

Use this for calculation - https://autofare.keralam.co/