May be the stem is 60mm. Hence the 60. As for 28mm tire width if there are no other markings lay the tubes next to each other and see if they are close. Most tubes fit a range of widths. Like 25mm to 28mm. Or 28mm to 32mm.

What brand of tube? Can you post a few pictures of the box.

Edit. Here are a few I have.

The Victoria on the left is for 18 to 23 mm
The Conti in the middle fit a wide range of 700 tires. 25 to 33.
The Conti on the left is the in between size.
One can use a tube outside the desired size range but more chance of a flat.