How can we convert a galvanometer into a voltmeter?

An ammeter whose resistance is $180\,\Omega$ gives full scale deflection when the current is $2\,mA$. The shunt required to convert it into an ammeter reading $20\,mA$ (in $\Omega$) is

The current sensitivity of a moving coil galvanometer increases by $20 \%$ when its resistance is doubled. Calculate,by what factor does the voltage sensitivity change?

$A$ galvanometer has a coil of resistance $200 \Omega$ with a full scale deflection at $20 \mu A$. The value of resistance to be added to use it as an ammeter of range $(0-20) mA$ is: (in $Omega$)

For designing a voltmeter of range $50\,V$ and an ammeter of range $10\,mA$ using a galvanometer which has a coil of resistance $54\,\Omega$ showing a full scale deflection for $1\,mA$ as in figure.
$(A)$ for voltmeter $R \approx 50\,k\Omega$
$(B)$ for ammeter $r \approx 0.2\,\Omega$
$(C)$ for ammeter $r \approx 6\,\Omega$
$(D)$ for voltmeter $R \approx 5\,k \Omega$
$(E)$ for voltmeter $R \approx 500 \Omega$
Choose the correct answer from the options given below

$A$ moving coil galvanometer has $N$ number of turns in a coil of effective area $A$,and it carries a current $I$. The magnetic field $B$ is radial. The torque acting on the coil is: