Have you ever wondered how a toaster knows how long to wait before popping the toast up? When you press the toast lever down, an RC circuit is connected to a voltage source. Current runs through this RC circuit until the capacitor reaches 90 percent of its full charge, at which point another component allows the toast to pop back up. The "darkness" knob on the front of a toaster is really a variable resistor, a type of resistor whose resistance changes between a minimum and maximum setting as you turn the knob. The RC circuit is made up of this variable resistor and a regular 1.80e-5 F capacitor. What is the (a) maximum and (b) minimum resistance that the variable resistor needs to provide in order for the "toasting" to last between 30 and 90 seconds?