Given :
(i) $MnO _{4}^{-}+8 H ^{+}+5 e ^{-} \longrightarrow Mn ^{2+}+4 H _{2} O \quad E ^{0}=x_{1} V$
(ii) $MnO _{2}+4 H ^{+}+2 e ^{-} \longrightarrow Mn ^{2+}+2 H _{2} O \quad E ^{0}= x _{2} V$
Find $E ^{0}$ for the following reaction :
$MnO _{4}^{-}+4 H ^{+}+3 e ^{-} \longrightarrow MnO _{2}+2 H _{2} O$
(A) $x_{2}-x_{1}$
(B) $x_{1}-x_{2}$
(C) $\frac{5 x_{1}-2 x_{2}}{3}$
(D) $\frac{2 x_{1}-5 x_{2}}{3}$