Answer:
Fern will knit 32 scarves in 8 nights.
Step-by-step explanation:
Number of scarves knitted by Fern in 5 night = 20
Relation between number of scarves knitted and number of nights is proportional,
Therefore, Number of scarves knitted (s) ∝ Number of nights spent to knit the scarves (n)
s ∝ n
s = kn
k = 
Here, k = proportionality constant
For s = 20 and n = 5,
k = 
k = 4 scarves per night
For 8 nights, by using the same proportionality rule,
k = 
4 = 
s = 32 scarves
Therefore, Fern will knit 32 scarves in 8 nights.