Find $y(5)$ if $(x,y)$ solves Lotka-Volterra system $(x',y')=(x-xy,xy-y)$ with $(x(0),y(0))=(600,800)$

Question

I don't remember well, but I was doing a biology problem using some Lotka-Volterra equation.

I had $\displaystyle\frac{dx}{dt}=x-xy$ and $\displaystyle\frac{dy}{dt}=xy-y$.

$y(0)=800$, $x(0)=600$, compute $y(5)$

But how do I solve? Do I just take the derivative of $\displaystyle\frac{dx}{dt}$ to get $\displaystyle\frac{d^2x}{dt^2}=2-3y-3x(4xy-y)$?

To get $\displaystyle \frac{d^2x}{dt^2}=2-3y+3xy-12x^2y$?

But I don't even know where and or how to solve...

I know Laplace Transform and separation methods.