Answer
$i=0.75mA$
Work Step by Step
We know that torque in a magnetic field is given by:
$T=i A B$
$i=\frac{T}{AB}$
Also, Area $A=0.04\times 0.04=0.0016m^2$
We plug in the known values in the formula above to obtain:
$i=\frac{4.8\times 10^{-8}}{0.0016\times 0.040}$
$i=0.00075$
$i=0.75\times 10^{-3}$
$i=0.75mA$
