How much cardio should i do a day to lose belly fat.?

Hi,
I need to lose about 8 kilos(17lbs) of belly fat. I want to lose i fast, by that i mean in about 2 and a half weeks. I already did 30 minutes on the exercise bike this morning and was sweating like a dog. How much more should i do tonight..
Thanks
Sorry, my bad, i actually want to lose it in 2 and a half months, i accidentally write weeks.