what's a good goal...

okay so I am at 140 lb ( 5'5-5'6" ) it took me 5 months (Aug-Dec) to lose 20 lb. I really want to make a goal weight for the summer but I don't know how much I can lose by May.

can I drop another 15-20 lb in 5 months or is this time going to take longer than previously?

did anyone take as long as me to lose weight?