Find the transfer function $\frac{Y(s)}{X(s)}$ of the system given below
1. $\frac{G_{1}}{1-HG_{1}} + \frac{G_{2}}{1-HG_{2}}$
2. $\frac{G_{1}}{1+HG_{1}} + \frac{G_{2}}{1+HG_{2}}$
3. $\frac{G_{1}+G_{2}}{1+H (G_{1}+G_{2})}$
4. $\frac{G_{1}+G_{2}}{1-H (G_{1}+G_{2})}$