Six Second Grade Students Tried Tossing a Ball into a Basket

Six second grade students tried tossing a ball into a basket ten times each. Their teacher tl suggested a different way of tossing the ball, and the six students tried again. The numbel successful tosses, before and after the teacher's suggestion, are shown below.
$\begin{array}{c|cccccc}\text { Student } & \mathbf{A} & \mathbf{B} & \mathbf{C} & \mathbf{D} & \mathbf{E} & \mathbf{F} \\\hline \text { Before the suggestion (out of 10) } & 5 & 3 & 5 & 2 & 5 & 3 \\\text { After the suggestion (out of 10) } & 3 & 3 & 3 & 3 & 3 & 3\end{array}$

Find the negative rank sum. [Recall, differences of zero are not ranked.]

A) -3.5
B) -1
C) -9
D) -1.5