Grammar - Who or Whom Continued

I put this in a comment on the first 'who or whom' post. I thought I would upgrade it to a post just in case you don't read the comments!

Another easy way to remember which word is right is this:

If you can use she/he in a sentence the correct word to use is who.

If you can use him/her in a sentence the correct word is whom.

So in case of your sentences it would go like this:

He/she is your college room mate - Who is your college room mate.

I would like to room with him/her - With whom do you want to room with.

He/she is/was the driver of the car - Who is/was the driver of the car.

Do you know if he/she was the driver of the car? - Do you know who the driver of the car was.