Answer
$-1.8J$
Work Step by Step
The work done by spring is negative as the motion is downward while the force of spring is acting upward.
$W_{spring}=-\frac{1}{2}Kx^2$
$K=\frac{2.5N}{cm}$=$\frac{2.5N}{cm}$.$\frac{100cm}{1m}=250\frac{N}{m}$
Now put the values
$W_{spring}=-\frac{1}{2}\times250\times(0.12)^2$
$W_{spring}=-1.8J$
