i do NOT understand at all desperate need of help !!

Lets first look at the cost per round with the 25 round pass
Take the total cost and divide by the number of rounds
$84 / 25 rounds
$ 3.36 per round
OR
They can pay 3.25 per round with the single pay
$3.25 is less than 3.36 so it is cheaper ( less per round) to pay the single round price
Option 2 $3.25 is cheaper