How long will it take me to lose 25-30 pounds?

OH MY GOD don’t listen to those awful spammers! I am so sick of them!!

Anyway, I commend you for wanting to lose weight. That is great that you are motivated to do this. Do not resort to diet pills or get thin quick schemes like starving yourself. Those two things will make you gain back extra weight once you stop those.
What exercises you should do are the following:

Aerobics- any activity longer than 30 minutes that uses the legs
ex. walking, running, jogging, jumping on trampoline, jumprope, jumping jacks, walking, biking, elliptical

This will blast the fat off of your body. It will gain little muscle.
Runners, walkers, bikers, are really thin, lean people.

Muscle training- don’t panic! You won’t get big and bulky like those weight trainers. For each extra lb of muscle you have, you lose extra calories, even in your sleep! So, use 2 or 3 lb dumbbells and lift them. There are arm exercises online you can practice. You can also do leglifts, and situps (please, use an exercise mat so you don’t hurt yourself.) Do a search for these online.
Since you are a girl, and you don’t want to bulk up, you won’t. Just aim for less weight, more reps (reps are the times you lift the weight.)

If a boy wants more muscle, use bigger weights and less reps. (Weight until your muscles almost give out to stop.) The tear in the muscles will repair, making the muscles bigger.

I hope this all helps and you are young, don’t let stupid spammers that show you websites tell you any differently than the healthy way.

By the way, you will stay skinnier longer if you lose 2 lbs a week. If you lose a ton of weight rapidly, it will come back on just as fast.

Good luck!