if PLUT price is $1, when User A deposits 10,000 PLUT tokens, borrows 2,500 pUSD (C-ratio is 400%). When C-ratio is down to 300% (meaning PLUT unit price is down to $0.7 per token), users will be required to repay the debts to a minimum C-ratio of 300%: 1, she/he can deposit extra 625 PLUT tokens; 2, she/he returns 312.5 pUSD borrowed.