Answer:
Suppose that you initially have $100 to spend on books or movie tickets.
The books start off costing $25 each and the movie tickets start off costing $10 each.
a. Your budget increases from $100 to $150 while the prices stay the same.
Increase
b. Your budget remains $100, the price of books remains $25, but the price of movie tickets rises to $20.
Decrease
c. Your budget remains $100, the price of movie tickets remains $10, but the price of a book falls to $15.
Increase