Solving a joint variation problem where z varies jointly as y and x, with the final answer z = 45/2 or 22.5.
A math problem on joint and combined variation, showing the solution for finding z when z varies jointly as y and x, with z = 12 when x = 2 and y = 4, and calculating z when y = 3 and x = 5, resulting in z = 45/2 or 22.5.