a)339 Cal to kilowatt-hours

It is important to distinguish Calories (with a capital C) from gram-calories.

339 Cal = 339,000 cal = 1.417*10^6 J

1 J = 1 Watt*second. For kW*h, multiply by 10^-3 kW/W * 1h/3600 s

I get 0.394 kWh