How much weight can I lose on this?

I'm starting the Special K Diet on Monday (tomorrow). I'll be eating a bowl of Red Berries with Lactaid for breakfast and lunch until July 17th. For dinner I'll have a small portion of whatever my mom or dad makes. If I'm hungry in between meals I'll probably have a small bowl of salad with 2 tablespoons of fat free dressing. I've already lost 10 pounds by eating 1200 calories and exercising daily, but I want to jump start my weight loss because I've come to a plateau. How much weight can I lose? I'm 14, 4'9, and weight 115 pounds.