Work is considered as the Force performed on a body to move it a certain distance, that is
W = Fd
Here
W = Work
F = Force
d = Distance
In this case we have the values of work and distance, therefore clearing for the Force we would have to
[tex]F = \frac{W}{d}[/tex]
Replacing,
[tex]F = \frac{3.2J}{8m}[/tex]
[tex]F = 0.4N[/tex]
Therefore the force that Marissa must exert on the windows shade is 0.4N