Moving Charges and Magnetism question for JEE Main (JEE Main 2025 (2 Apr, Shift 2)), with solution

In a moving coil galvanometer, two moving coils $M_1$ and $M_2$ have the following particulars:

$R_1 = 5\ \Omega$, $N_1 = 15$, $A_1 = 3.6\times10^{-3}\ \text{m}^2$, $B_1 = 0.25\ \text{T}$

$R_2 = 7\ \Omega$, $N_2 = 21$, $A_2 = 1.8\times10^{-3}\ \text{m}^2$, $B_2 = 0.50\ \text{T}$

Assuming that the torsional constants of the springs are the same for both coils, what will be the ratio of voltage sensitivity of $M_1$ and $M_2$?