In the given circuit, the equivalent resistance between A & B is ( if A has negative potential and B has positive potential)

$\Rightarrow$  -Ve polarity reaches to P side of  $D_1$, then $D_1$ diode is in Reverse bias
 $\Rightarrow$ +Ve polarity reaches to P side of  $D_2$, Then $D_2$ diode is in forward bias

   $R_2,R_3$   are in series
    $R_{23}=R_2+R_3=6+8=14\Omega$
 $R_{23},R_4$    are in parallel   $R_{234}=\frac{R_{23}\times R_4}{R_{23}+R_4}$  
                                $R_{234}=\frac{14\times 10}{14+10}=\frac{140}{24}=\frac{35}{6}$

$R_1\&R_{234}$   are in series   $R_{234}=R_1+R_{234}$
                               $R_{1234}=6+\frac{35}{6}=\frac{36+35}{6}=\frac{71}{6}$