Reasonable Goal?

What do you think is reasonable goal for me?
I am an 18 year old women, 5' 8- 5'9, with a medium-ish frame. I workout and lift weight, so I have a decent amount of muscle. Right now I weigh 148 and I'm not happy with it. I would like to weigh 130-135. Do you think is is a reasonable goal, if now what do you think would be?
Thanks! :)

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