Let a and b be two vectors such that |2 a +3 b |=|3 a + b | and the angle between a and b is 60^°. If 1/8 a is a unit vector, then | b | is equal to:

Let $\displaystyle \vec{a}$ and $\displaystyle \vec{b}$ be two vectors such that $\displaystyle |2 \vec{a}+3 \vec{b}|=|3 \vec{a}+\vec{b}|$ and the angle between $\displaystyle \vec{a}$ and $\displaystyle \vec{b}$ is $\displaystyle 60^{\circ}$. If $\displaystyle \frac{1}{8} \vec{a}$ is a unit vector, then $\displaystyle |\vec{b}|$ is equal to :