Some equipotential surfaces are shown in fig. The electric field strength is

$\mathrm{E}=\frac{-\mathrm{dv}}{\mathrm{dx}}$

$E=-\frac{10-20}{5\times {10}^{-2}\times \sin {30}^0}V/m=400 V/m$

$$\begin{gathered} \mathrm{as} \mathrm{the} \mathrm{direction} \mathrm{of} \mathrm{electric} \mathrm{field} \mathrm{is} \mathrm{perpendicular} \mathrm{to} \mathrm{equipotential} \mathrm{surface} \\ \mathrm{and} \mathrm{along} \mathrm{the} \mathrm{direction} \mathrm{of} \mathrm{decreasing} \mathrm{potential} \mathrm{so} \mathrm{it} \mathrm{makes} \mathrm{an} \mathrm{angle} \\ {120}^0 \mathrm{with} \mathrm{the} \mathrm{positive} \mathrm{x} \mathrm{axis} \end{gathered}$$