The following table of data represents how the brightness of a Wolf-Rayet ring nebula behaves as the nebula expands. Plot the given points on a graph withSurface Brightnessas the y-axis andRadiusas the x-axis. Then, draw a best fit smooth curve through the data. Use the curve to answer the questions on the below.

Radius (parsecs)	SurfaceBrightness (pc cm-6)
0.0	12.0
0.5	7.1
1.0	5.3
1.5	4.7
2.0	4.5
2.5	3.6
3.0	3.2
3.5	2.8
4.0	2.4
4.5	2.3
5.0	2.1
6.0	1.7
7.0	1.3
8.0	1.1
9.0	0.8
10.0	0.6

9. If it were impossible to see a ring nebula with a surface brightness fainter than 1.6 pc cm^-6, how big would the nebula be when it becomes invisible?:

parsecs

10. What would the surface brightness of a ring nebula be if it has a radius of 3.25 parsecs?

pc cm^-6