Following rule 2,  group gets third priority over methyl.

Here, for C₁ , the priority order is set to be as follows.

Following rule 1, hydroxyl group gets first priority.

Following rule 3, ethenyl group gets second priority ahead of R and methyl groups.

Following rule 2, R group gets priority over methyl.

Since, in this case, the lowest priority group is on the plane and not below it, so, it is converted to an identical form by keeping one of the groups on plane constant and rotating the other 3 groups clockwise. Now, it can be seen that the configuration is S.

Here, the priority order is decided as follows:

Following rule 1 bromo gets first priority
Following rule 2, R gets second priority
Following rule 2, methyl gets third priority.