In a double pipe cocurrent heat exchanger, operating at steady state, oil (specific heat capacity = $2100\text{ J kg}^{-1}\ ^\circ\text{C}^{-1}$) entering at $7\text{ kg s}^{-1}$ at $100\ ^\circ\text{C}$ is used to heat water (specific heat capacity = $4200\text{ J kg}^{-1}\ ^\circ\text{C}^{-1}$) flowing at $3.5\text{ kg s}^{-1}$ from $20\ ^\circ\text{C}$ to $50\ ^\circ\text{C}$. If the overall heat transfer coefficient is $291\text{ W m}^{-2}\ ^\circ\text{C}^{-1}$, the required heat transfer area (in $\text{m}^2$) is _____ (rounded off to one decimal place).