JEE Advanced Model Paper 8 with solutions for online practice

In a spark plug which is connected to the secondary coil if transformer an emf 40000V is inducedwhen in primary coil current changes from 4A to 0 in 10 10µs . The self inductance of secondary coil is1000H. Find the minimum value of self inductance of primary coil is 10−x µH. Then find x .