radius=3 4/5?

$$\textcolor[rgb]{1,0,0}{\text{Diameter}=}$$

$$3\frac{4}{5}*2=\left(\frac{3*5+4}{5}\right)*2=\frac{19}{5}*2=\frac{19*2}{5}=\frac{38}{5}=\frac{35+3}{5}=$$  $$\frac{35}{5}+\frac{3}{5}=7+\frac{3}{5}=\textcolor[rgb]{1,0,0}{7\frac{3}{5}}$$

 

S.

The radius is half way across the circle and the diameter is the whole way (through the centre)

diameter=2*radius 

$${\mathtt{diameter}} = {\mathtt{2}}{\mathtt{\,\times\,}}\left({\mathtt{3}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{4}}}{{\mathtt{5}}}}\right) \Rightarrow {\mathtt{diameter}} = {\mathtt{7.6}}$$ units