The quantity of charge $q$ (in coulombs) that has passed through a surface of area $2.00 \mathrm{cm}^{2}$ varies with time according to the equation $q=4 t^{9}+5 t+6,$ where $t$ is in seconds. (a) What is the instantancous current through the surface at $t=1.00 \mathrm{s} ?$ (b) What is the value of the current density?