(a) Work done = Area covered in between force displacement curve and displacement axis
= Mass $\times$ Area covered in between acceleration-displacement curve and displacement axis
$= 10 \times \frac{1}{2}\left( 8 \times 10^{- 2} \times 20 \times 10^{- 2} \right) = 8 \times 10^{- 2}J$