ESDU Challenge: Calculating Mach

a.

700 kn = 1296.4 kilometers per hour
Speed of sound at standard conditions ca. 1225 km/h

This will get less at heigth and with lower temperature.

So its not C)

To quote the wiki:

So, an aircraft traveling at Mach 1 at 20°C or 68°F, at sea level, will experience shock waves in much the same manner as when it is traveling at Mach 1 at 11,000 m (36,000 ft) at −50°C or −58F, even though it is traveling at only 86% of its speed at higher temperature like 20°C or 68°F

This means we are not to far off from A)

Speed of sound about 1050 km/h --> about 1.2 Mach

Easy enough. Speed of sound at altitude and temperature...

KTAS = 29.06 √(518.7 - 3.57*32.8084kft) = 582.3 kts @ 32,808.4ft

700/582.3 = 1.202 mach

Assumes that temperature at altitude = -3.57°F for every 1,000ft and 59° F as standard temperature at sea level.

32.8084kft = 32,808.4 ft or 10,000 meters altitude

Speed of sound on air at 10km height is around 1075 km/h, that is 0.88 times the sea level speed of sound. Now the mach ratio is relative to that local sound speed. Doing the math, the closest value from those given is a). S.M.

Forgot where I left my E6B...