The potential difference $\left(V_A-V_B\right)$ between the points A and B in the given part of the circuit

The figure shows currents in a part of electric circuit. Then current I is

A galvanometer may be converted into ammeter or a voltmeter. In which of the following cases the resistance of the device so obtained will be the largest?

A galvanometer has resistance $80 \Omega$ and it is shunted with resistance $20 \Omega$. If $20 \%$ of the main current flows through galvanometer, then what is the value of main current?