Anumber of simple sugars may combine to form:
a. protein.
b. complex carbohydrates.
c. amino acids.
d. fat.

The correct answer for this question is letter B. A number of simple sugars may combine to form complex carbohydrates. Complex carbohydrates are also called polysaccharides. Examples of simple sugars are glucose and fructose while starch is an example of complex carbohydrates.

You may be trying hard to make something difficult out of something easy here.

You have said that  a(n) = 8n .  (I can't write a subscript 'n'on this site either,
but  'a(n)'  will serve the same purpose.) 

So . . . (get ready) . . .

a(n) = (8) times (n)
a(1) = 8
a(2) = 16
a(3) = 24
a(4) = 32
a(5) = 40
a(6) = 48
.
.
a(100) = 800
a(101) = 808
.
.
etc.