Your diameter is 11.6 and as the radius is half of the diameter so ur radius will be half of the diameter !
so to find the radius as half means deviding by 2 we will find ur radius by deviding the diameter by 2 that will give us the half!
so we'll do it like this :
11.6/2
=5.8 ANSWER
I hope uv understood by now and if not then pls be free to ask!
I hope this helps as there was no question for me to answer so I thought this one I can do so let me answer this only !