When the weight on a string is changed from 4Kg to 10Kg,the elongation changes from 0.3mm to 0.7mm,how much work done during this extension of the string?($g=10m/s^2$)

Question

$\begin{array}{1 1}(A)\;41mJ\\(B)\;29mJ\\(C)\;20.5mJ\\(D)\;\text{None of above}\end{array}$