First option is to modify Z_1 so that its phase angle is decreased to less than 90deg by placing a resistor in parallel with the capacitor.   
The value of the resistor R_1 in parallel with capacitor = 5000 ohm
 
 The second option is to modify the phase angle of arm 2 or arm 3 by adding series capacitor   
The value of the reactance of the capacitor used, X_C = 200 ohm