Simple. Do nothing as it is already rounded to the nearest 100.
frist one 755 next 850 thid 725 frouth 855
900
800
It is 800 to the nearest hundred.
750 rounded to the nearest 100 is 800
800
It is 800.
800
To the nearest 100 it is 800
845 rounded to the nearest hundred is 800. Rounded to the nearest 10 is 850
700.
900
800
The smallest number that would round up to the nearest 100 to make 800 is 750.