If $f: \mathbb{R}^2\rightarrow\mathbb{R}$ where $F(x,y)=f(x+3y,2x-y)$ with $f$ is defferentiable and $\nabla f(0,0)=(4,-3)$ compute the derivate at the origin in the direction of unit vector $\vec{v}=(\frac{\sqrt{2}}{2},\frac{\sqrt{2}}{2})$

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Hi, I have some problems with this, it is possible that some concepts are flying on my mind but I don't know how I could solve the problem, help me? thanks