A bicycle racer rides with constant speed around a circular track 30 m in diameter. What is the acceleration of the bicycle toward the center of the track if its speed is 9 m/s?

Center-seeking force, aka Centripetal Force:

Here's a centripetal force calculator for you:
http://hyperphysics.phy-astr.gsu.edu/HBASE/cf.html

Hope that helps!