b
Potential difference between any two points in an electric field is given by,

\({\mathrm{d} \mathrm{V}=-\vec{E} \cdot \overrightarrow{d x}}\)

\({\int_{V_{O}}^{V_{A}} d V=-\int_{0}^{2} 30 x^{2} d x}\)

\({V_{A}-V_{O}=-\left[10 x^{3}\right]_{0}^{2}=-80\, \mathrm{J} / \mathrm{C}}\)