Can someone teach me how to do this step by step and give another example?

What step by step problem do you need shown?

The sun's parallax would be 180 degrees, greater than which you can't get.  so a. would be your anwser 

Geothermic gradient is the rate of increasing temperature with respect to increasing the depth in the earths interior. away from tech tonic plates boundaries, it is about 25-40 c/km (72-87 degrees f/mi) of depth near the surface in most of the world.