If not current flows through the galvanometer the find the value of unknown resistance X. Assume that resistance per unit length of wire AB is 0.2 `Omega//cm`.
then also calculate total current given by battery.

Explanation

For balanced condition `(X)/( R_(AJ))=(2)/(R_(JB))`
`R_(AJ)=0.02xx60=1.2Omega,R_(JB )=0.02xx4 0= 0.8O mega rArr(X)/(1.2)=(2)/(0.8)rArrX=3Omega`
Current given by the battery `I=(4)/(R_(eq))`
where `R_(eq)=((3+2)(1.2+0.8))/(3+2+1.2+0.8)=(10)/(7)Omega` so `I=(4xx7)/(10)=2.8A`