Which should be calculated first to solve this story problem?

the local bookstore has $500 to spend on new books each month. in january, it bought 20 copies of a new music book for $12.50 each, 15 copies of a new travel book for $9.95 each, and it donated $45.50 to the local children's charity. how much money did the bookstore spend on books in january?

a.
the total amount donated to charity each year

b.
the total amount spent on music books or on travel books

c.
the total amount the bookstore has to spend on books each year

d.
the amount of money left over after buying the books