It is 7800.
Most schools wrongly teach you to always round 5 up (so the answer would be 7900) but, while this is a simple rule to teach, it is not really correct. Under this rule:
100
0
97 rounded to the nearest hundred is 100. 97 rounded to the nearest ten is 100
300
200
853 rounded to the nearest 100: 900. 10853 rounded to the nearest 100: 10900.
600
100
100
0
555 rounded to the nearest 100 is 600.
97 rounded to the nearest hundred is 100. 97 rounded to the nearest ten is 100
100
100
100
0
300