The balanced condition for Wheatstones bridge is QP=SR
as is obvious from the given values.
No, current flows through galvanometer is zero.
Now, P and R are in series, so
Resistance, R1=P+R =10+15=25Ω
Similarly, Q and S are in series, so Resistance R2=R+S =20+30=50Ω
Net resistance of the network as
R1 and R2 are in parallel i=RV=500.6=0.36A