$(i)$ Combined sales in September and October for each farmer in each variety is given by

$A+B=$   $\left[ {\begin{array}{*{20}{c}}
  {{\text{ Basmati }}}&{{\text{ Permal }}}&{{\text{ Naura }}} \\ 
  {15,000}&{30,000}&{36,000} \\ 
  {70,000}&{40,000}&{20,000} 
\end{array}} \right]\,$ $\begin{matrix}
   {}  \\
    \mathrm {Ramkrishan} \,\,\,\,\,\,\,\,\,\,\,\,\,  \\
  \mathrm {Gurcharan}\,\,\mathrm {Singh}  \\
\end{matrix}$

$(ii)$ Change in sales from September to October is given by

$A-B=$   $\left[ {\begin{array}{*{20}{c}}
  {{\text{ Basmati }}}&{{\text{ Permal }}}&{{\text{ Naura }}} \\ 
  {5000}&{10,000}&{24,000} \\ 
  {30,000}&{20,000}&{0} 
\end{array}} \right]\,$ $\begin{matrix}
   {}  \\
    \mathrm {Ramkrishan} \,\,\,\,\,\,\,\,\,\,\,\,\,  \\
   \mathrm {Gurcharan}\,\,\mathrm {Singh}  \\
\end{matrix}$

$(iii)$  $2 \%$ of $\mathrm{B}=\frac{2}{100} \times \mathrm{B}=0.02 \times \mathrm{B}$

$=0.02 \left[ {\begin{array}{*{20}{c}}
  {{\text{ Basmati }}}&{{\text{ Permal }}}&{{\text{ Naura }}} \\ 
  {5000}&{10,000}&{6000} \\ 
  {20,000}&{10,000}&{10,000} 
\end{array}} \right]\,$ $\begin{matrix}
   {}  \\
    \mathrm {Ramkrishan} \,\,\,\,\,\,\,\,\,\,\,\,\,  \\
   \mathrm {Gurcharan}\,\,\mathrm {Singh}  \\
\end{matrix}$

$= \left[ {\begin{array}{*{20}{c}}
  {{\text{ Basmati }}}&{{\text{ Permal }}}&{{\text{ Naura }}} \\ 
  {100}&{200}&{120} \\ 
  {400}&{200}&{200} 
\end{array}} \right]\,$ $\begin{matrix}
   {}  \\
    \mathrm {Ramkrishan} \,\,\,\,\,\,\,\,\,\,\,\,\,  \\
   \mathrm {Gurcharan}\,\,\mathrm {Singh}  \\
\end{matrix}$

Thus, in October Ramkishan receives Rs. $100$, Rs. $200$ and  Rs. $120$ as profit in the sale of each variety of rice, respectively, and Grucharan Singh receives profit of Rs. $400$,  Rs. $200$ and  Rs. $200$ in the sale of each variety of rice, respectively.