Turn all rational numbers into fractions:
0.2 remains as it is
4/15 as a decimal is 0.26 with the 6 repeating
0.21 remains as it is
1/4 as a decimal is 0.25
Now we can organize from least to greatest as shown below:
0.2, 0.21, 0.25 (1/4), 0.2666666 (4/15)
Hope this helped!