I like to use the trick "Keep it, change it, flip it." for division of fractons. So keep 6/11 how it is, change the division sign to multiplication, and change 2/5 to 5/2, (Basically just flipping it.) Now multiply like how you would multiply fractions. Multiply numerators , (6 and now 5) by eahother and denominators, (11 and now 2,) by eachother as well. You get 30/22, which simplifies to 15/11. The mixed number version is 1 and 4/11 if you need that instead.
I hope this helps so that you don't have to search it up again!
The radius is half of the diameter. To find the circumference, use the equation C=2(pi)r or C=(pi)d. r meaning radius. d meaning diameter. (pi) is about 3.14 or 22/7
