We will solve this using Pythagoras theorem.
ㅤㅤㅤ➙ H² = P² + B²
Here, we have :
➝ H² = P² + B²
➝ P² = H² - B²
➝ x² = 17² - 15²
➝ x² = 289 - 225
➝ x² = 64
➝ x = √ 64
➝ x = 8