$16 billion every day will make it 5.84 trillion per annum.
Karachi is no longer the highest contributor to GDP it comes at second number after Lahore.
Assuming Lahore contributes only 1 rupee more than Karachi that would add another 5.84 trillion.
Tri-cities (Silakot, Gujranwala, and Gujrat) combined contribute the highest, assume tey contribute 1 rupee more than Lahore that would make another 5.84 trillion. Now forget all other cities like Faisalabad, Hyderabad, Peshawar, Questta still the total would become 17.52 trillion. Whereas Pakistans total GDP for 2012 is around 7.46 trilliion.
Either you have no idea how many zeros are there in a billion or this figure came from the head office of master of all trades, Altaf Hussain Tun.
There is nothing mythical about numbers, you can add them and see if they m,ake any sense, rather than believing every brain fart of some corrupt politician.