Hint: Draw 2 equal rectangular boxes. One on top of the other. Each represents the money she had at first.

Divide the first box into 4 fries, 2 chips and $0.30.

Divide the second box into 2 fries, 3 chips and $2.40.

Cancel 2 fries and 2 chips from each box.

Know that each fries is $2.80.

Find the cost of one bag of chips. (Ans: $3.50)

Another way :

4 - 2 = 2

If Geraldine only bought 2 packets of fries instead of 4 in the first case, she would have an extra 2 packets of fries' worth of money leftover.

2 x $2.80 = $5.60

She would have $5.60 more than now.
$5.60 + $0.30 = $5.90

She would have $5.90 remaining instead.

So if she buys 2 packets of fries , 2 packets of chips, she has $5.90 left.

Compare that to buying 2 packets of fries, 3 packets of chips, and having $2.40 left.

Thank you everyone..