Colour band $A$ and $B$ indicate the first two significant figures of resistance in 'ohm', while the $C$ band gives the decimal multiplier i.e., the number of zeros that follows the two significant figures $A$ and $B$.

The last band $D$ indicates the tolerance in percentage about the indicated value or in other word, it represents the percentage accuracy of the indicated value. 

For $R_1$, the given colour of the rings of a carbon resistor are orange, red, brown then, the value of resistance is

$R_1=32\times {10}^1$

Condition for balance in the Wheat stone's bridge is

$\frac{R_1}{R_3}=\frac{R_2}{R_4}$

So, $\frac{320}{R_3}=\frac{80}{40}$

$\therefore R_3=160 \mathrm{\Omega }$, so colour coding of resistor $R_3$ is

Brown$\to 1$

Blue$\to 6$

Brown$\to 1$
$16\times {10}^1\Rightarrow 160 \mathrm{\Omega }$