Can you please help with this question?

Acircle has a circumference of 28.36 units what is the diameter of the circle

What adds to be the bottom number but also multiplies to be the top number with 8 on the bottom and 15 on top

Determine the required value of the missing probability to make the distribution a discrete probability distribution. x p(x) 3 0.23 4 ? 5 0.51 6 0.08 p(4) = nothing  (type an integer or a decimal.)