8.403
That would be 8.403 - When rounding up or down, always look at the next digit. If it's between 0 & 4, you round the figure down (or just discard the digits you don't need) - if it's between 5 & 9, you round up to the next digit.
34921.000
31.623
3.330
The number 66.514 is already rounded to the nearest thousandth.
1.171
8.924
It is 6.981 when rounded to the nearest thousandth
34921.000
88.564
70.659
0.370
145 is rounded to the nearest ones. 145 rounded to the nearest thousandth is 145.000
800.130
174.689
8.246
287.287
32.346