Thanks for your reply. Unfortunately, I am still in the dark as I can not understand how you arrived at the numbers. I am a very elderly man, long past remembering math and I ask that you help me through the equation step by step. Thank you.
ok we need to multiply out the bracket.
so we get
right? get it?
which give us 0.4728r on the left hand side and 0r on the right hand side.
then we just need to divide 0.4728 to find r.
that will leave us
put that in your calculator or do the division by hand.
3s.f. means 3 significant figures.
Hope this helps.