Ana is solving the problem -15 + 42 using colored tiles. She is using red tiles to represent negative numbers, and yellow tiles to represent positive numbers. After representing the expression, she removes all zero pairs from her mat. How many tiles will be on her mat at the end of the problem? What color will they be? A.
15 red tiles

B.
27 red tiles

C.
27 yellow tiles

D.
57 yellow tiles