The equivalent resistance between $A$ and $B$ for the mesh shown in the figure is

When the resistance is connected in series then the formula of equivalent resistance, $R=R_1+R_2+R_3+....+R_n$, but when they are connected in parallel then net resistance is, $\frac{1}{R}=\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}+...+\frac{1}{R_n}$, so in the above diagram the equivalent resistance will be, 

,

in the above branch, resistance are connected in parallel, so new equivalent resistance will be, 

So, the final resistance will be, $R_{net}=\left(4+4+8\right) \mathrm{\Omega }=16 \mathrm{\Omega }$.