In $\Delta ABC$ $a=3,b=5,c=6$ find the value of $\sin\large\frac{A}{2}$

Question

$(a)\;\sqrt{14}\qquad(b)\;\large\frac{1}{\sqrt {14}}$$\qquad(c)\;\sqrt{15}\qquad(d)\;\large\frac{1}{\sqrt{15}}$