Let $P(2\sqrt{3},\frac{5}{2})$ is any point on the ellipse $\frac{x^2}{16}+\frac{y^2}{25}=1$ having centre C. Let Q and R are feet of perpendiculars from foci $S_1$ and $S_2$ on the tangent at P, tangent at P intersects y-axis at T and N is the foot of the perpendicular from centre C on the normal at P and  intersects major axis and minor axis at A and B, then the value of $\left(CA\right)\left(CT\right)+\left(PN\right)\left(PB\right)$ is equal to