Got Cragars, will this backspacing work or do I need to exchange?

[HunterRotten]

My mom bought me a beautiful set of Cragars from a car show she attended with my dad. They took about two months to arrive. They bought two 15x8's and two 15x10's. These are pretty standard sizes for these trucks, and everyone says this size will work. However, the wheels came with a backspacing that is a bit off.

If anyone could tell me what "OS" and "CB" mean that'd be great too.. The 15x8's have same Backspacing/"CB" however have a "OS" of -6. 15x10 have "OS" of -32

Incase this website decides to flip the photos around for me, I'll post the information as given on the 15X10 box.

CRAGAR
61C515042
15x10.00 5/5.00 S/S Chrome 362
OS=-32 BS=4.250 CB=3.579

IF this backspacing is going to be alright, will it work with a 295/50/15 on the rear and 255/60/15 on the front?

Thanks for the help, guys!