Answer: 140% change (40% increase)
Step-by-step explanation:
To calculate the change, you can divide the new value (21 books) by the old value (June). This will result in a change of 1.4, which is 140% when you convert it to a percentage (by multiplying by 100). To get the secondary answer («40% increase»), you can subtract 100 to get your percent of change.
