The exercise I tried to solve in the picture I attached is a convultion integral that should be solved for 0<=t<3 where u(t) is the step function (0 for all negative numbers and one for other numbers) and d(t) is the Dirac function. Can anyone see anything wrong with my resolution cause the coeficient i called A should be independent of t and the fact is that I cant see where my mistake is. Anyone can see my error?

thank you