derivative with e^: F(x) = (x + e^-3x)^2

[Nerd187]

I'm having trouble getting this answer.

If F(x) = (x + e^(-3x))^2, then F'(0) = ...?

My work:

2 (x + e^(-3x)) (1 + e^(-3x)) (-3), and then plug in 0 for x

I basically did the Chain Rule twice, but I'm getting an answer of -12, and the answer is supposed to be -4. I don't know how to get it, or where I'm going wrong.

 

[pka]

The derivative is:
\(\displaystyle \L
2\left( {x + e^{ - 3x} } \right)\left( {1 - 3e^{ - 3x} } \right).\)