\(2 + 4x - 12 = 0\)
\(4x = 10\)\(x = \frac{{10}}{4}\)\(x = \frac{5}{2}\).
$xMn{O_4}^ - \, + \,y{H_2}S{O_4}\, \to \,2M{n^{2 + }}\, + \,5{H_2}O\, + \,z{e^ - }$