1. The problem statement, all variables and given/known data
Find the function satisfying the differential equation:
dy/dx - 3y = 6e^(5x)
with y(0) = -6
2. Relevant equations
I believe this is Linear, so it is dy/dx + P(x)y = f(x)
3. The attempt at a solution
I chose -3y to be P and used it to obtain integrating factor e^(-3x). I multiplied it though and ended up with d/dx(e^(-3x)y) = 6e^(2x)
I integrated both sides and got e^(-3x)y = 3e^2x + C
Solving for C gets me -9 so the satisfying function is y=e^(3x)(3e^(2x)-9)
When I try to input this function into Webwork (online homework), it tells me it is incorrect and that the variable 'x' is not defined in this context.
I wanted to make sure I am correct or if somehow, x comes out of this equation.