Well, just looking at this problem we know 3 formulas that will help us. Firstly we have C (The Circumference) is Equal to 2π Times the Radius, r.
In Equation form that looks something like this:
C=2πr
We also know that the radius is half of the diameter, r=D/2 or D=2r
So, if C=62.8, then 62.8=2πr must also be true.
By doing some quick re arranging we get to the equation r=62.8/2π
This equation gives us 9.99, Which is essentially 10.
Now that we know that r=10, we can find that diameter, D=2r, is Equal to 20.
Therefore, your answers are
Radius = 10
Diameter = 20
Circumference = 62.8 (Given)
If there are any questions about anything I did please feel free to ask more questions and I will respond ASAP!