A 400V, 50 kVA, delta connected synchronous motor with the synchronous reactance of 3 Ω is supplying a 12 kW load with an initial power factor of 0.86 lagging. The windage and frictional losses are 2 kW and core losses are 1.5 kW. Now if the flux is increased by x % we will get an excitation voltage of 500 V. Then the value of x is ____%