Partial Derivatives: f(x,y)=e^(3x+9y) Find fsubxx

[MathNoob123]

Homework Statement

f(x,y)=e^(3x+9y)
find fsubxx

Homework Equations

The Attempt at a Solution

I got e^(3x+9y)3, but the stupid web assign won't take it as an answer. I am pretty sure this is the correct answer. Am i wrong? Please help =).

 

[S_Happens]

First, I would reorder the way you write the answer to avoid confusion.

Second (hint), what is the difference in f_x and f_xx