+12mm offset 15x7 wheels?
 

So i ordered some wheels through work today. was checking out the part number online tonight, and found they are 15x7 with +12 mm offset. wondering if thats close to 4.5 inchs of backspacing everyone runs. i noticed the part number above it is a -6mm offset. So what does offset have to do with backspacing? did i get the right wheels? or should i have got the -6mm offset for the 4.5inchs of backspacing?
:

heres a link to the wheels
they are the series 84 daytona
Steel Wheels | CECO Distributors Ltd.

https://blazerforum.com/forum/tires-...ry-rims-51432/

Check out the pic on Post #7 of this thread

Looks like they are 3.5 backspacing