Linda Simpson

My Rx350 2014 says I can use E10 and premium only. I’m confused? They are completely different fuels aren’t they? Should I use as much of the premium fuel I have in the tank before I refill with E10 if this is they way I decide to go? Or does it not matter if u mix the two. I’m about to do a 400km drive and don’t want any issues in the drive. Any advice would be greatly appreciated. Linda