So, the school Im going to next year requires each person to play a sport or join a club, and I want to join the BMX racing team. I can mountain bike really well, but BMX racing is a totally different thing. Is there anyone who does BMX races could help me get started by recommending some gear or bikes? Thanks! (and yes to all the moderators, this is school related)

Apinhole camera is made out of a light-tight box with a piece of film attached to one side and pinhole on the opposite side. the optimum diameter d(in millimeters) of the pinhole can be modeled by d=1.9[ (5.5 x 10^-4) l) ] ^1/2, where l is the length of the camera box (in millimeters). what is the optimum diameter for a pinhole camera if the camera box has a length of 10 centimeters