As you read this in your chair, how fast are you moving relative to the chair? relative to the sun?

To answer this question, you need to know the definition of Relative Motion:
 The motion is relative when it depends on a reference point or referencial system. If you know the reference point, you can determine the velocity of an object.
 If you are sitting on your chair, you are not moving relative to it (Your speed is 0 km/s); but as you know, our planet moves around the Sun (Traslation Movement) with a speed of 30.0 km/s. Therefore, you are moving 30.0 km/s relative to the sun.

Iagree c would be the answer