Given numbers : 0.209, 0.039, 0.21, 0.045 .
In order to check the smallest number, we need to check tenth value of each number first.
0.209 has 2 in tenth place, 0.039 has 0 in tenth place, 0.21 has 2 in tenth place and 0.045 has 0 in tenth place.
In first step, we got two smaller numbers 0.039 and 0.045 because they both have 0 in tenth place and other two numbers 0.209 and 0.21 has 2's in tenth place.
Now, we will check hundredth place number in 0.039 and 0.045.
0.039 has 3 in it's hundredth place and 0.045 has 4 in it's hundredth place.
Therefore, 0.039 would be smallest number and 0.045 would be second smaller number.
Now, we woiuld check hundredth place number in 0.209 and in 0.21.
0.209 has 0 in it's hundredth place and 0.21 has 1 in it's hundredth place.
Therefore, 0.209 is smaller than 0.21 and third smaller number.
So, finally 0.21 would be greatest number.
So, the order from least to greatest is 0.039, 0.045, 0.209, 0.21 .
So, the order will be c < a < d < b.
