30-35,000 feet
The cruising altitude of a normal commercial jet airplane today is around 12,000 m (35,000 ft).
At cruise altitude (35,000ft) the average cruise speed is 460 knots - 530mph.
a Boeing 757 is a narrow body jet airliner
122 normal 120 high altitude
The 757 is a jet airplane. It does not have propellors.
A normal commercial jet can cruise at a speed of mach 0.85 or about 570 miles
from wikipediaCruise speed Mach 0.80 (530 mph, 458 knots, 850 km/h at cruise altitude, i.e. 35,000 ft or 10.66 km)
The 757 has a service ceiling of 42,000ft so it is legally capable of flying at any altitude up to 42,000ft
it depends on what kind of jet it is. 737 jet: 200 747 jet: 500 757 jet: 280 767 jet: 290 777 jet: 550 787 jet: 350
Narrow Body
The jet stream regularly affects high altitude wind and low altitude weather.