3. A round hole is to be cut using ECM through a plate of pure copper (valence = 1) that is 50 mm thick. The hole diameter is 10 mm on each side, but the electrode that is used to cut the hole is 7 mm diameter to allow for overcut. The applied current = 10 amps. Using an efficiency of 87%, determine how long it will take to cut the hole (C= 7.35 x 10-2 mm3/ A-s)