Help me with this please.

What are “like terms”? why can we only add like terms?

What will the graph look like for a system of equations that has no solution? a. the lines will be perpendicular. b. the lines will cross at one point. c. both equations will form the same line. d. the lines will be parallel.

The radius of the earth is two times the radius of the moon. what fraction of the volume of the earth is the volume of the moon?