#### Answer

$0.1m$

#### Work Step by Step

As we know that
$P.E=\frac{1}{2}kx^2$
but $P.E=mgh$
$mgh=\frac{1}{2}kx^2$
here in our case
$h=0.4+x$
Thus putting the values, we get
$2(9.8)(0.4+x)=\frac{1}{2}(1960)x^2$
$7.84+19.6x=980x^2$
$980x^2-19.6x-7.84=0$
after solving it, we get
$x=0.1$m