Transform to system of first order equations

[Taylor1234]

Homework Statement

u'''-8u''+2u'-3u=0

Homework Equations

The Attempt at a Solution

So I let:
x1 = u
then x1' = u'
x2 = u'
then x1' = x2
and x2' = u''
x3 = u''
then x2' = x3
and x3' = u'''

I have only done these problems with second order equations, so I don't understand which values I am supposed to plug back into the original equation. Any help is appreciated! Thanks!

 

[Defennder]

This problem is similar:
https://www.physicsforums.com/showthread.php?t=232512