Which of the following is the least? a.0.105b.0.501c.0.015d.0.15 i don't need an answer i need an explanation

I find the largest number by moving backwards. Tens, ones
In this case it would be 0.501, because it has the most tenths. So we cross it off
Then we find the new largest number
here it is 0.15 (the difference between that and 0.105 is that 0.105 does not have any hundredths, but the 5 is in the thousandths place.
Now we find the next one
Now it is 0.105
Then you only have one remaining answer, therefore 0.015 is the smallest answer!