You state in your first post that the Laplace transform of a function, f(x), is \(\displaystyle \int_0^\infty f(t)e^{-st}dt\). So why does the work you show not have any integrals?
The Laplace transform of \(\displaystyle f(x)= e^{-ax}\) is \(\displaystyle \int_0^\infty e^{-at}e^{-st}dt= \int_0^\infty e^{-(a+ s)t}dt\). Can you integrate that?
The Laplace transform of \(\displaystyle f(x)= Ax+ B\) is \(\displaystyle \int_0^\infty (Ax+ B)e^{-st}dt\). Integrate that using "integration by parts" with u= Ax+ B and \(\displaystyle dv= e^{-st}dt\).