You need to create a common denominator:
For these 1.5/6 , 1/3 and 4/9, 18 is a common denominator.
Multiply numerator and denominator by the same number to change each fraction to the common denominator:
1.5/6(3/3) = 4.5/18
1/3(6/6) = 6/18
4/9(2/2) = 8/18