A $0.80\,\text{m}$ steel wire and a $1.4\,\text{m}$ brass wire are connected end to end. The joined wires hang from a fixed support, and a force of $40\,\text{N}$ is applied, as shown. The Young modulus of steel is $2.0 \times 10^{11}\,\text{Pa}$. The Young modulus of brass is $1.0 \times 10^{11}\,\text{Pa}$. Each wire has a cross-sectional area of $2.4 \times 10^{-6}\,\text{m}^2$. The wires stretch without reaching their elastic limits. Determine the total extension. Ignore the weights of the wires.
- A$1.7 \times 10^{-4}\,\text{m}$
- B$3.0 \times 10^{-4}\,\text{m}$
- C$3.9 \times 10^{-4}\,\text{m}$
- D$9.0 \times 10^{-4}\,\text{m}$