An experiment uses microphone moving toward a speaker as a way to measure the speed of sound in different media. In air, the frequency heard by the moving microphone is 20% higher than the frequency of the sound when the microphone is at rest. When the gas in the experimental system is replaced by helium, the frequency heard by the moving microphone is now only 6.8% higher than when the microphone is at rest. Based on this information, what is the speed of sound in helium?

Independent variable is something that is changed in a experiment. 

You need to be more specific.  i really don't know what a "motion map" is.you can draw a graph of an object's position, distance, displacement, speed,velocity, or acceleration versus time, or you can draw a graph of the object's x-position versus its y-position and not give any information about time at all.if the graph presents position or displacement against time,  then constant velocity is a straight line . . i.e. a line that has  constant slope.if the graph shows speed against time, then constant velocityis a horizontal piece of line.if the graph shows acceleration against time, then constant  velocity is a piece of line that lies on the x-axis . . it's value is zero.