The answer depends on the units used for 39.51: It should be blindingly obvious to anybody that the answer for 39.51 hours and 39.51 milliseconds will be very different.
4000
36 seconds
40
40
36 seconds
36 seconds
SIC 3951 covers makers of Pens, Mechanical Pencils, and Parts
40.00
If that's seconds, it rounds to 40.
Establishments primarily engaged in manufacturing mechanical pencils are classified in SIC 3951
It is closer to 36 than it is to 35.
The two whole numbers on either side of 57.3 are 57 and 58. The first of these is 57.3 - 57 = 0.3 away while the second is 58 - 57.3 = 0.7 away. So cleary the first, 57 is the nearest whole number.