Solution:
Note that:
Simplify the equation to find the radius. Then double the radius to obtain your diameter.
The diameter of the circle is 1 unit.
[tex]\\ \tt\hookrightarrow \pi d=3.14[/tex]
[tex]\\ \tt\hookrightarrow 3.14d=3.14[/tex]
[tex]\\ \tt\hookrightarrow d=1[/tex]