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
i don't understand how to get answer can you help

Answer 1

5/4 = 1.25 >> amount paid for each card

5/3 = 1.67 >> amount received for each card

1.67 - 1.25 = 0.42 profit on each card.

100 / 0.42 = 238.1 = 239 cards to make a profit of at least $100.