Answer:
8.09
9.1 is obviously greater than 8.9, when you compare the numbers.
And the other numbers are all 8 in the ones place (to the left of the decimal). So, you have to look at the number in the tenths place (to the right of the decimal). 8.09 has a "0" in the tenths place, & 8.9 has a "9" in the tenths place, making 8.09 less than 8.9.
If you compared the 2 remaining numbers 8.91 & 8.99, they would both be greater, because since they all have the same number in the tenths place, you have to move on to comparing the next number, which would be in the hundreths place (2 digits to the right of the decimal).