Let the ages of Ishan and Anushka be the roots ($\alpha$ and $\beta$) of a quadratic equation. We are given:
A quadratic equation can be formed using its roots with the formula:
$ x^2 - (\text{sum of roots})x + (\text{product of roots}) = 0 $
Substituting the given sum and product into the formula:
$ x^2 - (18)x + (56) = 0 $
This simplifies to:
$ x^2 - 18x + 56 = 0 $
Comparing this equation with the given options, we find it matches option 4.
If $\frac{a+1}{a^2-1} = \frac{1}{5}$, then the value of $a$ is -