The  coercivity of a certain permanent magnet is $4.0\times {10}^4{\mathrm{Am}}^{-1}$ . The magnet is placed inside a solenoid 20cm long and having 700 turns and a current is passed in the solenoid to demagnetize it completely. The value of current x A. Then the value of 10 x.

The coercivity of $4\times {10}^4{\mathrm{Am}}^{-1}$ of the permanent magnet implies that a magnetic intensity $\mathrm{H}=4\times {10}^4{\mathrm{Am}}^{-1}$ is required to be applied in opposite direction to diamagnetic the magnet.
Here, $\mathrm{n}=\frac{700}{20\mathrm{cm}}=\frac{700}{20\times {10}^{-2}\mathrm{m}}=3500 \mathrm{turns} /\mathrm{mAs},\mathrm{H}=\mathrm{ni}\therefore \mathrm{Current},$
$\mathrm{i}=\frac{\mathrm{H}}{\mathrm{n}}=\frac{4\times {10}^4}{3500}=11.43\simeq 11.5\mathrm{A}$