A cyclotron is used to produce $16$ MeV protons which are directed at a transparent capsule containing $10$ g of nitrogen. If the target is irradiated uniformly with a flux of $10^10$ protons$/$cm$\mathrm{²}$ s for $50$ min, what is the activity of $11$C produced, given that cross$-$section is $=0\mathrm{.}085$barn.