The equation of a line is typically written as y=mx+b where m is the slope and b is the y-intercept. If you know two points that a line passes through, this page will show you how to find the equation of the line.
Since the pyramids are similar, the scale factor will be 3. So the height of the small pyramid is 6.3/3=2.1. The volume will be (1/3)*(2.1)*(2.3)^2=3.70
