A number of incandescent lamps are connected in delta across the lines of a balanced 230 V, 3-phase, 3-wire system. A sing-phase wattmeter is connected in the circuit. The current coil of the meter is connected in line 1 while the potential coil is connected across lines 1 and 3. This wattmeter registers 8.4 kW. If the potential terminal of the meter, which was connected in line 3, is transferred to line 2. The wattmeter reads 7.5 kW. If each lamp is rated 100 W, how many lamps are connected across lines 1 and 2. Assume lamp pf to be unity.