Concept: The question tests on application of overlapping sets

Solution:

Let there be 3 overlapping sets of Raisins, Almonds and Peanuts.
Let "only peanuts"=x
=>"only Raisins" = 10x
only peanuts is one-fifth the number of bags that contain only almonds
The number of bags that contain only almonds is 20 times the number of bags that contain only raisins and peanuts
Let number of bags that contain only raisins and peanuts =y
=>Only almonds = 20*y  =20y
=>Only peanuts= x= 1/5*20y  =4y
=>y=x/4
Total = 435 = (Almonds set) + 10x + y + x(This will represent the remaining values)
=>435 = 210 + 10x + x/4 + x
=>x = 20

The number of bags that contain only one kind of item
=10x + x + 5x
= 16x
= 320  (option d)

PS-Pls note
The question says there are 210 bags of almond and this count include not only the bags with "only" almond but also the count of bags that may contain almonds and raisins and/or almonds and peanuts and/or all the three.
210 is not the "only" almond count whereas 20y and 5x are.