From the manual of the ASRock website:
- 1 x CPU Fan connector (4-pin)
- 1 x Chassis Fan connector (4-pin)
- 1 x Power Fan connector (3-pin)
If you have the manual that came with the motherboard, go to page 12.
Seems you can use the #10 (Chassis Fan connector) and #26 (Power Fan connector).
If you don't have the manual, go here:http://www.asrock.com/mb/Intel/B75M-DGS/?cat=Manual
And download the User Manual