You're having coffee at the local Starbucks when hunky Mr. Brad Pitt walks in and orders a grande mocha latte with whipped cream. You whip out your cell phone camera to snap a pic of him slurping down his extravagant drink.

The flash unit for the camera has a capacitance of 1080e-6F. The flash unit is connected to the lithium cell phone battery. What resistance is needed in this RC circuit if the flash is to charge to 81.0% of its full charge in 20.3 s? (20.3 is the time. 20.3 is not the time constant.)