10645

Is it R? or S?

1st priority: COH
and which one is second priority?

10645

Is it R? or S?

1st priority: COH
and which one is second priority?

That is R.
2nd priority is the tertiary C.

This would be R configuration. You are right about the first priority, the second would be (CH3)3C because the C is attached to 3 other C's and the last one would be the propyl group... This gives S, but since H is facing out of the page, you reverse the config. and it is R...