First, you have to split 56 in half (because Lena bought 4 more than half of 56) 56 divided by 2 equals 28. Then you add 4 because again, Lena bought 4 more than half. That ends up at 32.
To find Jodie's bottles, you have to do 56 - 32, because the remainder of the bottles belongs to Jodie. I got 22.
Jodie bought 22 bottles of nail polish.