What is the fastest way to lose weight, I want to lose 12-15kgs (26-33lbs) in 3 months?

I'm 18, I'm 179 cm, about 5'9 or 5'8, I'm 77 kilos which is 170 pounds, there's this girl I'm meeting in summer and I want to be in shape by then :D , ehhh I have a treadmill and two 5 kgs dumbbells, thats 10 pounds, it would be better if I could do exercises at home as I'm busy with college and there's no time to go to the gym, I was thinking of following these P90X videos but I don't know, what do you tihnk? I want to lose weight more from waist and under, can a treadmill do that or does it have to be a stepper?