Answer
given,
wavelength (λ)= 500 n m
thickness of film= 10⁻⁴ cm
refractive index = μ = 1.375
distance traveled is double which is equal to 2 x 10⁻⁴ cm
a) Number of wave


N = 2.91
N = 3
b) phase difference is equal to
Reflection from the first surface has a 180° (½λ) phase change.
There is no phase change for the 2nd surface reflection and there is no phase difference for the 2nd wave having traveled an exact whole number of waves.
net phase difference = 
= 270°
Answer:
i only wrote this for points
Explanation:
Lets write again formula for determening Ann's performance.
P = 70.443 + 4,885*t
where t is in hours. This is equation with P(t) which means that P only depends on variable t. If we express t=2.6 in formula we will find her expected performance.
P = 83.144
Now, since it says that she scored 16 points less than expected we need to find value of P-16
P - 16 = 67.144
After round we get that the answer is 67