Who told you that you have 8.9 acres? Relatives, operator, deed, purchase offer?
If it is in the deed, then its net mineral acres. Ideally you should know that you own X% of Y acres in Z location. Mineral acres. Sounds like you are leased (to SPC I presume), do you have a copy of the lease and/or bonus check information? Bonus is paid on net mineral acres.
The only people that would mention net royalty acres would be the people trying to buy your minerals.