There are two ways to solve this.
The first way is logically.
Mary can
-wear a pink dress with black shoes -wear a pink dress with white shoes
-wear a blue dress with black shoes -wear a blue dress with white shoes
-wear a yellow dress with black shoes - wear a yellow dress with white shoes
Count them up, and you'll get six combinations!
Another way is simply mathematically, which is easier in my opinion.
3 (different colored dresses) × 2 (different colored shoes) = 6 (combos)
