PHRASAL VERB DRILLS

account for something
ex) Can you account for those nice cars?
ex) I'd like to account for the answer.
ex) Is it hard to account for the book?

Here is a link from thefreedictionary.com which may help you in understanding this word (http://www.thefreedictionary.com/account). It has many meanings.

The way you used 'account' here sounds a little awkward or stiff, not natural. In English we use 'account for' in this way-

Phrasal Verb: account for 

1. To constitute the governing or primary factor in: Bad weather accounted for the long delay.

2. To provide an explanation or justification for: The suspect couldn't account for his time that night.

add up
ex) I want to add up how many times you take a the medicine.
ex) She will add it up how many hours I spend the time in this hotel.
ex) Could you add up that how many balls have you you have carried?

Good work! English grammar can be really confusing. I find Korean grammar challenging, so I'm really impressed that you are trying to grasp the concept behind Phrasal Verbs, which are some of the most difficult to understand verbs in English!

PHRASAL VERB DRILLS

account for something
ex) Can you account for those nice cars?
ex) I'd like to account for the answer.
ex) Is it hard to account for the book?

add up
ex) I want to add up how many times you take a medicine.
ex) She will add it up how many hours I spend the time in this hotel.
ex) Could you add up that balls have you carried?

Am I going right way?