Problem #$8$: Let $y(x)$ be the solution of the initial$-$problem

$y^{(4)}+4y^{\text{'}\text{'}}=0$

$y(0)=0,y^{\text{'}}(0)=5,y^{\text{'}\text{'}}(0)=0,y^{\text{'}\text{'}\text{'}}(0)=-8$

Enter the function $y(x)$ into the answer box below.