If $y=79e^{5x}+85e^{-5x},$ then :

$\frac{d^2y}{dx^2}=79y$ $\frac{d^2y}{dx^2}=10y$ $\frac{d^2y}{dx^2}=5y$ $\frac{d^2y}{dx^2}=25y$

$\frac{d^2y}{dx^2}=25y$