A 17 W energy-efficient fluorescent lamp is designed to produce the same illumination as a conventional 68 W lamp. How much does this energy-efficient lamp save during 64 h of use? Assume a cost of $0.77/kW · h for electrical energy. Answer in units of dollars.

vapour or gas assuming atmospheriv pressure

a skateboard rolling across the street - apex

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me