Let a vector \( \vec{a} \) has magnitude \( 9 \). Let a vector \( \vec{b} \) be such that for every \( (x,y)\in \mathbb{R}\times\mathbb{R}-\{(0,0)\} \), the vector \( (x\vec{a}+y\vec{b}) \) is perpendicular to the vector \( (6y\vec{a}-18x\vec{b}) \). Then the value of \( \left|\vec{a}\times\vec{b}\right| \) is equal to: