Using your mouse identify the x,y coordinates for two points using the yellow line segment on the sail.
Name these two points E and F.
Point F should be to the right of Point E.

Point E (x coordinate): Point E (y coordinate):

Point F (x coordinate): Point F (y coordinate):

From these two points calculate the slope, then the length of your line segment using the distance formula.
Remember, the origin(0,0) is the bottom left corner of the picture.