You have to do a substitution. You're integrating, or solving the equation, which is, of course, the final goal. But this problem is just an exercise in generating first-order systems of equations from higher-order equations - something that definitely has practical value for numerical work. For the first equation, let
Then write two equations that are the equivalent of Hint: is already one of them.
The y equations will work in much the same way. What do you get?