1. The problem statement, all variables and given/known data Determine whether the system is linear 2. Relevant equations Superposition 3. The attempt at a solution I am comfortable solving the case where the bounds are from negative infinity to t. I have provided an example of that solution I found online. I attempt to solve that problem in a similar fashion and conclude the system is linear, but according to the solutions (no work just answers) I was provided with the system is not linear. I would appreciate if someone could tell me where I went wrong (why the same procedure can't be applied) or whether I am correct.