Weight and diet help!!?

I'm 14 and need to lose some weight. I have 51 days to lose 25-30 pounds! I NEED to lose it by the 4th august and KEEP it off. what are some of the best activities/exercise to do and some i could do at home since i don't have much money to buy anything. Also what food is healthy, low is cals and is filling as this is my only downfall, is eat because I'm worried bout my tummy rumbling coz thats soo embarressing!!! don't say i should want to lose that much weight or anything like that so only reply if is going to be helpful. I am currently as size 12 and want to be a size 8. Thanks :)