Spring constant for original spring is -
K=W/9
Since, K is inversely proportional to length,
Therefore spring constant of spring of length 40cm is
=60/40 K =3/2K
And that for spring of length 20 cm is
=60/20K =3K
Combination of two springs is
3/2K + 3K = W
9/2 K = W
We know that K=W/9
So W=9/2K*x
9K = 9/2K*x
X=2cm