The answer to the question is B) velocity i.e the quantity described here is velocity.
Step-by-step explanation:
Before coming into any conclusion, first we have to understand a vector quantity.
Vector quantities are the physical quantities which not only require magnitude but also direction for their complete specification. It is also in accordance with parallelogram law of vector addition.
As per the question, the truck is travelling at 30 mph to the west.
Here, 30 mph is the magnitude of the quantity which is nothing else than the distance covered per hour. So, it represents the speed of truck.
The truck is also moving towards west which gives the direction of motion of the truck.
We know that speed in a given direction is called velocity.
Hence, the correct answer to the question will be velocity.