Electrical power companies sell electrical energy by the kilowatt-hour, where 1 kWh = 3.6x106 J.
Suppose that it costs $0.15 per kWh to run your
electric water heater. How much does it cost to heat
75 kg of water from 15°C to 43°C to fill a bathtub?

Aproduction line at v. j. sugumaran's machine shop has three stations. the first station can process a unit in 7 minutes. the second station has two identical machines, each of which can process a unit in 16 minutes (each unit only needs to be processed on one of the two machines). the third station can process a unit in 10 minutes. ▼ is the bottleneck station, with a bottleneck time of nothing minutes per unit (enter your response as a whole number).