You can write and solve the proportion
[tex]\dfrac{256\,\text{cars}}{6\,\text{hours}}=\dfrac{x\,\text{cars}}{10\,\text{hours}}\\\\x\,\text{cars}=(10\,\text{hours})\cdot\dfrac{256\,\text{cars}}{6\,\text{hours}}=426\frac{2}{3}\,\text{cars}[/tex]
The appropriate choice is ...
... a. 426