Answer
${\bf 0.672}\;\rm T$
Work Step by Step
We know that Hall voltage is given by
$$\Delta V_{\rm H}=\dfrac{IB}{tne}$$
So the magnetic field strength is given by
$$B=\dfrac{tne\Delta V_{\rm H} }{I}$$
Plug the known;
$$B=\dfrac{(1\times 10^{-3})(2.1\times 10^{21})(1.6\times 10^{-19})(120\times 10^{-3}) }{(60\times 10^{-3})}$$
$$B =\color{red}{\bf 0.672}\;\rm T$$
