Drive Your Car $5.0 \mathrm{~km}$ Due East At $35 \mathrm{~km} / \mathrm{hr}$

drive your car $5.0 \mathrm{~km}$ due east at $35 \mathrm{~km} / \mathrm{hr}$ and suddenly realize that you forgot your wallet. So, you return home, driving west at $40 \mathrm{~km} / \mathrm{hr}$ , and upon arrival you spend 10 minutes looking for it. Finally, you get back on the road and drive a total of $57.0 \mathrm{~km}$ due east. If your average velocity was $40 \mathrm{~km} / \mathrm{hr}$ for the whole journey, what was your average speed during the last leg?

A) $45 \mathrm{~km} / \mathrm{hr}$
B) $40 \mathrm{~km} / \mathrm{hr}$
C) $49 \mathrm{~km} / \mathrm{hr}$
D) $58 \mathrm{~km} / \mathrm{hr}$