The best estimate is always the exact answer since it is always possible to improve upon any other estimate.
150/30 = 5
5
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...
17.0429
20.3897
38
106.8333
The best estimate is the true value.
31.8321
2981.35
0.975
1/80
1/80
87.0484
7.875