The best estimate is always the exact answer since it is always possible to improve upon any other estimate.
45/9 = 5
247.6667
20.8
What's "best" depends on what you are going to use this for. You can take a calculator and do the exact calculation. Or you can round the numbers in a way that makes it easy to do the calculations in your head.
2.2360...
106.8333
17.0429
38
20.3897
The best estimate is the true value.
31.8321
2981.35
0.975
7.875
1/80
1/80
87.0484