$\begin{aligned}
& f(x+y)=f(x) \cdot f(y) \
& \Rightarrow f(x)=e^{\lambda x} f^{\prime}(0)=4 a \
& \Rightarrow f^{\prime}(x)=\lambda e^{\lambda x} \Rightarrow \lambda=4 a
\end{aligned}So,f(x)=e^{4 x}\begin{aligned}
& \mathrm{f}^{\prime \prime}(\mathrm{x})-3 \mathrm{af}{ }^{\prime}(\mathrm{x})-\mathrm{f}(\mathrm{x})=0 \
& \Rightarrow \lambda^2-3 \mathrm{a} \lambda-1=0 \
& \Rightarrow 16 \mathrm{a}^2-12 \mathrm{a}^2-1=0 \Rightarrow 4 \mathrm{a}^2=1 \Rightarrow \mathrm{a}=\frac{1}{2}
\end{aligned}$ 
F(x)=e2x Area =∫02exdx=e2−1