well, if you look at the picture, the "radius" is 1/4, so r = 1/4.
[tex]\bf \textit{diameter of a circle}\\\\
d= 2r\qquad \boxed{r=\frac{1}{4}}\implies d=2\cdot \cfrac{1}{4}\implies d=\cfrac{1}{2}\\\\
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\textit{circumference of a circle}\\\\
C=2\pi r\qquad \boxed{r=\frac{1}{4}~,~\pi =\cfrac{22}{7}}\implies C=2\left( \frac{22}{7} \right)\left( \frac{1}{4} \right)
\\\\\\
C=\cfrac{2\cdot 22\cdot 1}{7\cdot 4}\implies C=\cfrac{11}{7}\\\\
-------------------------------\\\\[/tex]
[tex]\bf \textit{area of a circle}\\\\
A=\pi r^2\qquad \boxed{r=\frac{1}{4}~,~\pi =\cfrac{22}{7}}\implies A=\left( \frac{22}{7} \right)\left( \frac{1}{4} \right)^2
\\\\\\
A=\cfrac{22}{7}\cdot \cfrac{1^2}{4^2}\implies A=\cfrac{22}{7}\cdot \cfrac{1}{16}\implies A=\cfrac{11}{56}[/tex]
