Ihave a bunch of these and i don’t understand it at all

The correct option is: Option (B) 

Explanation:

First thing is that the difference between each number in the series with the next number is 5. It means it must be the multiple of 5. There are two options that contain multiples of 5: Option B and Option D. Now in the option D, the upper limit is 6. If we put 6 in the expression: 5(6)-2, the last term would be 28. However in the series given in the question, the last term is 33. Hence 5(7) - 2 = 35 - 2 = 33 which is Option B.

When i=1: 5(1)-2 = 3
When i=2: 5(2)-2 = 8
When i=3: 5(3)-2 = 13
.
.
When i=7: 5(7)-2 = 35-2 = 33
Hence the correct option is (B).

Both A and C are acceptable answers, because they will make either .8xoriginal servings or .2xoriginal servings.