Step 1: Idea:
Since $\sin^{-1}1=\pi/2$, the relation says the second inverse sine equals $\pi/3$.
Step 2: Solve:
Take sine of both sides: $\sqrt{3/x}=\sqrt3/2$. Squaring gives $3/x=3/4$, so $x=4$.
Step 3: Factor Check:
$x^2-x-12=(x-4)(x+3)$, whose roots are 4 and -3. So 4 is a root of option (B).
Final Answer:
Option (B).
\[ \boxed{\text{(B) } x^2-x-12=0} \]