An immersion heater used to boil water for a single cup of tea plugs into a 120 V outlet and is rated at 300 W. 

a. What is the resistance of the heater? 

b. Suppose your super-size, super-insulated tea mug contains 400 g of water at a temperature of 18°C. How long will this heater take to bring the water to a boil? You can ignore the energy needed to raise the temperature of the mug and the heater itself.