Generally speaking, you only need to do aerobic exercise for a long time every day, and the duration must be enough. In fact, 30 minutes is just a starting point to lose weight. You should keep doing it for at least 50 minutes. At the same time, your strength should be controlled well, not too low or too high. Medium speed will do. Jogging or brisk walking is a good choice. If you want to lose weight faster, you'd better do more aerobic and anaerobic strength exercises, because your condition will not be very effective. I can't say how much you can lose weight in three months, it depends on how you persist, preferably more than five days a week. If you want to know more, please follow my blog.