Distance from a Constant Velocity
Key Questions

Answer:
#d = v t# Explanation:
If you are given a constant velocity
#v# , then you can compute the distance traveled#d# if you also know the amount of time#t# that the object was traveling for. 
Answer:
A plot of distance over time will be a straight line at a slope equal to the velocity.
Explanation:
The equation is:
Distance = Velocity x TimeSo, a plot of distance over time will be a straight line at a slope equal to the velocity.

It depends on what you are given.
If you are given a distance function and it is linear, then the velocity is constant. If you are given a distance graph and it is linear (all lines below), then the velocity is constant. If it is strictly a curve, then velocity is not constant.
If you are given a velocity function and it is constant, then the velocity is constant. If you are given a velocity graph and it is horizontal (blue and green lines below), then the velocity is constant. If the graph is anything but horizontal, then the velocity is not constant.
If you are given an acceleration function or graph and it is zero (green line below), then the velocity is constant. If it is anything but zero, then the velocity is not constant.