The truck is described as travelling at 30mph to the west. the quantity described here is a(n)

Before going to get the answer first we have to understand Vector. A vector is a physical quantity which has magnitude as well as direction for its complete specification.

As per the question the truck is travelling at 30 mph to the west.

Hence the distance covered by the truck in one hour is 50 miles. It is the average speed of the truck. Here 50 mph is the magnitude of the average sped.

The direction of motion  of truck is towards west.

Speed is a scalar quantity.But speed in a given direction is called velocity which is a vector quantity .

As per the question the truck is moving 30 mph towards west which infers  the velocity of truck whose direction is towards west.

As we know that velocity is a vector quantity, so the quantity described here is a [vector].

Velocity is going to be your answer.

a lot of it means it can be "burned" for energy and sold at one price. if it is scarce, the price will go up