The formula for the circumference of a circle is:
C = 2(π)(r)
Here, you are given 319 as the C, so plug that into the equation.
319 = 2(π)(r)
Now solve. Divide both sides by 2π.
159.5/π = r
50.8 = r
The radius is half the diameter, so to find the diameter, jusy multiply the radius by 2.
50.8 × 2 = 101.6
d = 101.6
The diameter of the circle is 101.6.