@ ashutosh
its not a wheatstone bridge combination . so, we need to take series and parallel combination here .
3 ohm and 4 ohm are in series , and anathor 3 ohm and 5 ohm they are also in series with each other .
and the middle galvanometer arm are parallel with the two .
so, frst redraw the circuit . in which 1 resistance will be 7 ohm , and its parallel to 3 ohm and again the both are parallel to 8 ohm .
here i have applied series combination at frst R (equi ) = R1+R2
then u have now 3 resistor in parallel , now apply .
r ( equi ) = 1/ r1 + 1/r2 + 1/r3
which is
1/7 + 1/3 + 1/8 = 1/ R
then calculate the value of R ..
HOPE U CAN DO IT NOW
IF ANSWER NOT MATCHING THEN LET ME KNW . I
ALL THE BEST ..