Antoine wants to convert millimeter into kilometers which operation should he choose multiply 1000 divide 1000 multiply 1000000000 or divide 1000000000

How would doubling the made of an object change the objects potential energy

It is really hard for me right know

An important dimensionless parameter concerned with very high-speed flow is the mach number, defined as v/c, where v is the speed of the object such as an airplane or projectile, and c is the speed of sound in the fluid surrounding the object. for a projectile traveling at 1170 mph through air at 50 ˚f and standard atmospheric pressure, what is the value of the mach number?