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

Replacing,


Therefore the force that Marissa must exert on the windows shade is 0.4N
To solve this problem it is necessary to apply the concepts related to destructive interference.
The concept refers to an overlap of two or more waves of identical or similar frequency that, when interfering, creates a new pattern of waves of lower intensity
By definition destructive interference is given by

Where,

n=integer (1,2,3,4,5,6...etc)
t = thickness
M= Index of refrqaction
For minimum thickness to satisfy this condition n will be minimum there,
n=0
Therefore

Solving to find M,



Therefore the correct answer is B. 1.38