Quick ways to lose 20 pounds?

I'm 5'7 and a hundred and fifty-two pounds I do twenty sit ups everyday and walk a LOT, oh and I'm a vegetarian. I try to exercise as much as I can but even with exercising I've been unable to lose weight. My friend suggested I try doing something she use to do when she wanted to lose weight but I really don't think doing that is a good idea, so I was wondering is there anything else anyone can think of that I can do to help me lose around 20 pounds?
Quick ways to lose 20 pounds?
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