Sorting numbers combined with text

Hello,

I have read up on this topic, but need confimation that I am hosed. I have a project worksheet that I use as a "master lookup". For each project I am tracking, I may or may not have subsets (child projects) that do not sort properly. The nomeclature I use is 1301, 1302, 1303a, 1303b, etc. So, each project does not absolutely have subsets, but for those that do, when I sort, it sorts the proejcts with letters below the other data. I have tried everything in my power to reformat, to no avail.

I have tested whether or not excel, indeed, thinks like I expect it to (on a blank sheet,) and it normally does.

What can I do to resolve (See attached example)