The more honest you are with yourself here, the more accurate the outcome!

Try and be as specific as you can, but estimates are fine too.

If you don't know, just put in the National Minimum Wage
Are they out of the room compiling reports, looking at assessments, planning, catching up on observations, printing and photocopying etc..? If they use their break time, include this too.
Maybe they are cutting and sticking into learning g journeys, rewriting observations, cross-referencing, planning... etc.