1. **Problem:** How many triangular tiles are there in the FIFTH figure of the sequence? 2. **Understanding the pattern:** The problem states the sequence of triangular tiles increases as 13, 28, 16, 15 for the first four figures. We need to find the number for the fifth figure. 3. **Analyzing the given options:** a. 13 b. 28 c. 16 d. 15 4. Since the problem does not provide a direct formula, we observe the pattern of the number of tiles in the first four figures: 13, 28, 16, 15. 5. The sequence does not follow a simple arithmetic or geometric progression. However, the problem likely expects the answer to be one of the given options. 6. Given the pattern and the options, the most reasonable answer for the fifth figure is **15**. **Final answer:** 15