A certain reactant $B^{n+}$ is getting converted to $B^{(n+4)+}$ in solution. The rate constant of this reaction is measured by titrating a volume of the solution with a reducing reagent which only reacts with $B^{n+}$ and $B^{(n+4)+}$ . In this process, it converts  $B^{n+}$ to $B^{(n-2)+}$ and    $B^{(n+4)+}$ to  $B^{(n-1)+}$ . At t = 0, the volume of the reagent consumed is 25 mL and at t = 10 min, the volume used up is 32 mL. The rate constant of the conversion of $B^{n+}$   to $B^{(n+4)+}$  is x (in  ${\min }^{-1}$) assuming it to be a first order reaction. Find 100 x$(ln75=4.3,ln61=4.1)$ (Rounding to nearest integer)