Six Second Grade Students Tried Tossing a Ball into a Basket

Multiple Choice

Six second grade students tried tossing a ball into a basket ten times each.Their teacher then suggested a different way of tossing the ball, and the six students tried again.The
Number of successful tosses, before and after the teacher's added instruction, are shown
Below.
Ignoring the differences of 0, the positive rank sum is:

A) +9
B) +3
C) -4
D) +1