A horizontal rectangular surface has dimensions $3\mathrm{.}40$ cm by $4\mathrm{.}00$ cm and is in a uniform magnetic field that is directed at an angle of $31\mathrm{.}5$ above the horizontal.

Part A

What must the magnitude of the magnetic field be to produce a flux of $3\mathrm{.}90{10}^{-4}Wb$ through the surface?

Express your answer with the appropriate units.