If you push a chair across the floor at a cibstant velocity how does the force of friction compare with the force you exert?

-- "constant velocity"   ===>    acceleration is 0 .

-- acceleration=0   ===>   forces are balanced

-- balanced forces   ===>  (friction) + (force you exert)  =  0

                                           (friction) = -(force you exert)

                        They have equal magnitude and opposite direction. 

therefore, the efficiency is:

No because a circle or pie graph usually shows percentages you'd need a line graph