Out of every100 people, 20 now use public transport and 80 use cars.....
And of the 80 that use cars, 30% of these will switch to public transportation....thus.....the public transportation system will increase by 80 * .30 = 24 people out of every 100
However, it will also lose 10% of its current ridership to cars = 20 X .10 = 2 people out of every 100
So, the percentage of people using public transportation in the long run will be
[20 + 24 - 2] / 100 = 42%
