Answer: 1, 2, 4, 8 or 16 t-shirts.
Explanation:
1. To solve this problem you can find the factor pairs of 16.
2. By definition, factor pairs are two whole numbers that are multiplied to obtained a determined product.
3. Therefore, keeping the information above on mind, you must write the factor pairs whose product is 16. You have:
- She could have bought 1 t-shirt with a cost of $16:

- She could have bought 2 t-shirts, each one with a cost of $8:

- She could have bought 4 t-shirts, each one with a cost of $4:

- She could have bought 8 t-shirts, each one with a cost of $2:

- She could have bought 16 t-shirts, each one with a cost of $1: