Just to make sure we are talking about the same thing, c is a straight line between points X and Z, called the cord, the curved line would be called arc length XZ.
Assuming you know c (BEAM) (not XZ) and m then the formula would be:
r = (m² + ¼c²)/2m
This gives you the radius of the curve / Camber
m is the height of the of the camber.