6 is the correct answer because the thousandths place is a number of 5 and above, which means you move the hundredths place value up by 1. Because the hundredths place value is 9, moving it up by 1 would mean that 0 becomes the place value for the hundredths place and one is added to the tenths place. And because 9 is also the place value of the tenths place, the tenths place becomes 0 and 1 is added to the ones place.
