the picture in the attached figure
we know that
in the right triangle FON
sin F=opposite side angle F/hypotenuse
in this problem
opposite side angle F=ON--------> 9 units
Hypotenuse=FN--------> 18 units
so
sin F=ON /FN-------> sin F=9 /18
therefore
the answer is the option
B.) sin F 9/18
