How much should I be eating a day? Like Calories?

[springbuds]

And how do I work them out? I am 18 and 162lbs, and I am looking to get back to 110lbs which I was last year. I feel overweight, I wuld like peopl to be honest and say if I look it.
This is a picture of me now:
http://i288.photobucket.com/albums/ll168/bumpynights/weight/after.gif

Help!
Jst to add, as seem to be a little confusion in answer, I am female.

I have now booked a doctors appointment and will keep you updated.

[alialoggi]

What have you been doing differently for the past year that caused you to gain 52 lbs? That is what you need to stop doing! Or, you used to exercise and you stopped, then you need to exercise again. Aim for eating 1800 calories a day and do 1 hr of exercise a day. Take a work out class, start jogging (an excellent way to lose weight, trust me). Serious work outs, not bike riding which is more of an activity. Watch what you eat, make healthy choices and keep a food journal to keep you honest. Stop with the fast food and junk food. Eat lots of fruits and veggies with every meal. Good luck!