6.31 rounded to the nearest tenth is 6.3. When rounding, you look at the digit in the hundredths place (which is 1 in this case). Since 1 is less than 5, you do not round up, and the tenths place remains 3.
174.3
1.965 rounded to the nearest tenth is 2.0
236.6
20.1
It is: 58.1
8.1
31.8
18.2
55
0.4
10.0
6.70