In Problems $17-20,$ use Theorem $4\mathrm{.}4\mathrm{.}1$ to reduce the given differential to a linear first$-$order DE in the transformed function $Y(s)=L\{y(t)\}.$ Solve the firstorder DE and then find $y(t)=L^{-1}\{Y(s)\}.$ Use the table of Laplace transforms in Appendix C as needed. Note: Your solution may contain an arbitrary constant.

$17.t{y}^{\text{'}\text{'}}-y^{\text{'}}=2t^2,y(0)=0,y^{\text{'}}(0)=0$

$18.t{y}^{\text{'}\text{'}}-4t{y}^{\text{'}}-4y=0,y(0)=0,y^{\text{'}}(0)=5$