Light with an energy flux of $20 \mathrm{~W} / \mathrm{cm^{2}}$ falls on a non-reflecting surface at normal incidence. If the surface has an area of $30 \mathrm{~cm^{2}}$, the total momentum delivered during 30 minutes isa) $36 \times 10^{-5} \mathrm{~kg} \mathrm{~m} / \mathrm{s}$b) $36 \times 10^{-4} \mathrm{~kg} \mathrm{~m} / \mathrm{s}$c) $108 \times 10^{4} \mathrm{~kg} \mathrm{~m} / \mathrm{s}$d) $1.08 \times 10^{7} \mathrm{~kg} \mathrm{~m} / \mathrm{s}$