What does the expression “75 meters per second southeast” best describe?

Velocity because it has speed, along with direction.

Velocity is also a vector because it has both direction and magnitude.

Southeast is the direction of velocity while 75 m/s or instantaneous speed (meters per second) is the magnitude of velocity.

This is also equal to 270,000 meters an hour(m/h) or around 167.81 miles an hour(mph) or 270 kilometers an hour(km/h)

To convert seconds to seconds in an hour, multiply by 3600 because there are 60 seconds in a minute, and 60 minutes in an hour.

There are 1000 kilometers in an hour.

There are 1609.34 or 1609 meters in a mile so you divide this factor to get the miles per hour.

what is the question because that is not a question.

see the picture for the vector

the magnitude of the vector by pythagorean theorem

r = √( (-10)^2 + (3)^2 ) = √109

magnitude = √109 units

the direction angle between vector and x-axis is

tan^(-1)(3/10) = 16.699

so the direction is approximately 16.7 degrees north of west