The steel plate casting in Figure 2 is to be fed by a cylindrical riser with height equal to diameter. Using Chvorinov's rule (t = C(V/A)^{2}, same mould constant), the riser must take 25 % longer to solidify than the casting. Treat all faces of the casting and all faces of the riser (side, top and bottom) as cooling surfaces. Determine the riser diameter (answer in mm).