Given,
Equation of hyperbola 9x2−b2y2=1
And latusrectum LR subtends 60∘ at centre
Now, plotting the diagram we get,

Now, from above diagram we get A(ae,\frac{{b}^{2}}{a})&B(ae,\frac{-{b}^{2}}{a})
⇒tan30∘=aeab2=a2eb2=31
⇒e=93b2 as a2=9
Also, e2=1+9b2
⇒1+9b2=813b4
⇒b4=3b2+27
⇒b4−3b2−27=0
⇒b2=23+117 {ignoring the negative sign as it is a square function}
⇒b2=23(1+13)
Hence, on comparing with ml(1+n) we get,
⇒l=3,m=2,n=13
⇒l2+m2+n2=182