Final answer:
Aubrey has 9 buttons and gives away b buttons. The expression to calculate the buttons she has left is 9 - b.
Step-by-step explanation:
The student question asks about forming a mathematical expression to represent the number of buttons Aubrey has left after giving away some. Aubrey starts with 9 buttons and gives away b buttons. To express how many buttons she has after giving some away, we subtract the number of buttons given away from the original amount.
The expression that shows the number of buttons Aubrey has left is:
9 - b
Here, 9 represents the total buttons she started with, and b represents the number of buttons she gives away.