10a + b = 10b + a - 9
a + b = 11
3 is tenths
5 is hundredths
9 is thousandths
9.000 is the answer so 9 because 9.173 is part of a number or a unit.
90,000 vs 9000
10 times greater
In our (positional) numerical system, the first digit form the right represents the units, and going leftwards, every digit is worth 10 times more than its previous one.
So, in your number, the 9 to the right means "9 units", because it's the rightmost digit.
On the other hand, the leftmost 9 is worth 9 millions, because you shift 6 positions from the right, and the digits are worth:1st digit from the right: units2nd digit from the right: tens3rd digit from the right: hundreds4th digit from the right: thousands5th digit from the right: tens of thousands6th digit from the right: hundreds of thousands7th digit from the right: millions
answer: a and b