word problem need help:

Question

suppose you own a card shop. you buy one line of cards at a rate of 4 cards for $5.
you plan to sell the cards at a rate of
3 cards for $5
how may carfds must you sell in order to make a profit of $100.00
would it be 80 card?

Answer 1

profit per card = 5/3 - 5/4 = 5/12 or 41.666.. cents

number of cards ---- n
(5/12)n ≥100
n ≥ 1200/5 or 240

Answer 2

I don't understand you who did got this answer can you pls explain to me agian sorry im confused