Tatiana is buying b number of books and m number of magazines at the book fair. The books cost $4 each and the magazines cost $2 each. Tatiana's total purchase can be shown with this expression: 4b+2m. Which expression is equivalent to 4b + 2m?
A) 6bm
B) 2(2b+2m)
C) 2(2b+ m)
D) 6(b+m)