I have to find Green's function and solve the problem on $\displaystyle \mathbb{R}^+ \times \mathbb{R}^+$:

$\displaystyle \Delta u=0$
$\displaystyle u(0, x_2)=0$
$\displaystyle u(x_1, 0)=\frac{x_1}{1+(x_1)^2}$


Any hints will help..
Thank you.