Sixth Grade Round-Up

The entire sixth grade class gathered on the soccer field for a class picture. Since the photographer was not ready, the principal had all 360 students line up by height and form a circle. Helen was number 123, and her best friend, Monique, was directly opposite her in the circle. What number is Monique? Lucy was number 299, and her cousin, Linus, was directly across from her. What is Linus' number? Create a formula or rule that gives the number opposite any number in a circle. Write a rule that gives the number opposite any number no matter how many students are in a circle (assume there is always an even number of students.