[tex]\text{The standard form of the circle:}\\\\(x-h)^2+(y-k)^2=r^2\\\\\text{h and k are the x and y coordinates of the center}\\\text{r the radius}\\\\\text{we have}\\\\(x-16)^2+y^2=9\\\\r^2=9\to r=\sqrt9\to r=3[/tex]
[tex]\text{The diameter d is equal 2r. Therefore}\\\\d=2\cdot3=6[/tex]
