Given your current height/weight/age, you should be able to lose an average of 1.5 lbs. per week, assuming no cheating and you exercise regularly/properly. In a little over 11 weeks, that should amount to an approximate 17 lb. loss, plus or minus...which is probably close enough to your target of 20. So, yes, it should be possible, provided you don't go on and off your diet, and provided you stick with your exercise.
Another way to check your likely progress in the upcoming weeks is to see how much you have been losing (on average) over the past 4-6 weeks...although that approach presumes you have behaved yourself over the past 4-6 weeks.
Good luck!
20lbs in 11 weeks - can i?
