Explain one way in which friction actually helps people

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. 

Blue light reflected from the ball enters human eyes.

When calculating percentage we need two numbers. one number represents total amount of certain thing and another number represents partial number of that thing. then we divide those two numbers.in this problem total amount represents total number of weeds growing on some surface. partial number represents chicory.percentage = partial / total * 100%percentage = 29 / 98 * 100%percentage = 29.6%our calculation is closest to answer b) so this is our correct answer.