If You See the Notation ,What Should You Do

Multiple Choice

If you see the notation ,what should you do?

A) First multiply each X by its partner Y,then sum the results.
B) First sum the Xs then multiply the sum of the Xs by each Y.
C) First sum the Ys,then multiply the sum of the Ys by each X.
D) First sum the Xs,then sum the Ys,then multiply the sums.