Economics: The total cost C of electricity for a particular light bulb varies jointly as
the time t that the light bulb is used and the cost k per
kilowatt-hour, and C = 12¢
kilowatt-hour. When t=50 h and k= 6 ¢ per kilowatt hour. Find C to
the nearest cent when t =
30 h and k = 8¢ per kilowatt-hour.

Please show how you found answer.
It’s number 8.