Doing it freehand I got about 9 knots.
Starting at the right hand edge 1300 ft is 2 small squares above the bold sloping line that is between the two arrow heads.
The sloping lines are almost parallel to each other, so going down to the bottom left end we should end up 2 small squares above the bold sloping line.
Draw a horizontal line to the left across the wind area.
At the left end of the graph the MSL and ISA lines cross 18.5 small squares up from the bottom of the graph.
Draw a horizontal line to the right from this point to the weight REF LINE. This should meet the REF LINE about 2 small squares below the bold sloping line that is below the two arrow heads.
Move to the right parallel to the bold sloping line until you are directly above the 3200 lb mark. The bold sloping line only goes down about half of a small square over this distance so you should now be 18 small squares above the bottom of the graph, directly above 3200 lbs.
Now draw a horizontal line to the right to meet the wind REF LINE. You should hit yhis line 18 small squares up from the bottom of the graph.
Move down to the left parallel to the wind lines until you cross the line that you drew from the right. Drop down to the bottom of the graph to read off approximately 9 knots.
The closest option to this, which is at least 9 knots is 10 knots.
This is the correct answer.