We need to find out what to do to get 12.6 from 4.5 or 4.5 from 1.5 and then check if the same operation will give us the same result on the other side of the ratio. In this case it's easy to realize that:
1.5 * 3 = 4.5
So if we have to multiply one side of the ratio by 3 to get the proportion, we should do the same with the other side:
4.5 * 3 = 13.5
It gave us 13.5 instead of 12.6, so we can surely say that 4.5 : 1.5 is NOT proportional to 12.6 : 4.5.
