Convert Time Value To Correct Hh:mm Time?

I have a row of cells, and some of which are displaying time, but in an incorrect format.

for example 15:20 is showing in a cell as 3.2

How can I create a new cells that basically converts 3.2 into 24 hr hh:mm ....e.g. 15:20?

If I got to use the format cells option, and hh:mm, it changes the cell to the completely wrong time (i.e 04:48) ?

p.s. I should state that "some" of the cells are kind of showing the correct time, albeit with a decimal instead of a colon, for example, cell A12 is showing 4.25

one other thing I should mention.....the times will always be PM...... so 3.2 should be 15:20, and not 03:20