[tex] \frac{a}{sin a}= \frac{b}{sinb} = \frac{c}{sin c} = 2R
[/tex]
[tex] \frac{BC}{SIN A}= \frac{AC}{SIN B} = \frac{AB}{SIN 60} =2R
[/tex]
[tex] \frac{4}{ \frac{ \sqrt{3} }{2} } =2R
2R* \sqrt{3}/2 =4 = R \sqrt{3} =4
R= 4/ \sqrt{3} = 4 \sqrt{3}/3 [/tex]