A 240-V, 20 hP, 850 r.p.m., shunt motor draws 72A when operating under rated conditions. The respective resistance of the armature and shunt field are 0.242 ohm and 95.2 ohms, respectively. Determine the percent reduction in the field flux required to obtain a speed of 1650 r.p.m., while drawing an armature current of 50.4 A. (9)