Acity has a population of about 6759000. to which place is the number rounded?

Try looking at the question like this.
You have 0 tenths (00)
You have 0 hundreds (000)
You have 9 thousands (9000)
You have 50 thousands, (50,000)
You have 700 thousands (700,000)
You have 6 millions (6,000,000).
To determine which number it is rounded to, simply look at which has an actual number in it. 9,000ths is the first slot with a number, which means the number is rounded to the nearest thousand. If it was 6,759,800, it would be rounded to the nearest hundredth and so on...