The 24 inch shelve is 2 feet ( 1 foot = 12 inches)
She bout 7 feet of shelves (5 + 2 = 7)
The total cost for the shelves was 7 x 1.25 = $8.75
She spend an additional 90 so her total spent was 90 + 8.75 = $98.75
Now subtract her total from 100 to find the amount of change:
100 - 98.75 = 1.25
The change was $1.25