The electric field in a region is given by $\vec{E}=(A x+B) \hat{i}$, where $E$ is in $N C^{-1}$ and $x$ is in metres. The values of constants are $A=20 \mathrm{SI}$ unit and $B=10 \mathrm{SI}$ unit. If the potential at $x=1$ is $V_1$ and that at $x=-5$ is $V_2$, then $V_1- V_2$ is :
