Would it have been wrong to take a different approach with calculating the revenues?

The approach I took was, I tried to calculate the total daily revenue through calculating the revenues from the night and day shift separately.

Firstly,

no. passengers per day = (airport passengers) * (percentage of passengers using taxi)/ (days in a year)

= 84M*20%/350

= 48,000 passengers

That means,

daytime shift = (total taxis used in day) * dayfare

= (no. of passengers per day * % of day passengers)/passengers/taxi * dayfare

assuming on average a taxi is shared between 2 passengers

= (48,000* 50%)/2 * 70

= 840,000

Night shift = (total taxis used at night) * dayfare

= (no. of passengers per day * % of night passengers)/passengers/taxi * dayfare

assuming on average a taxi is shared between 2 passengers

= (48,000* 50%)/2 * 80

= 960,000

Total Daily Revenues = 840,000+960,000 =1.8M