anyone know how to do this

Answer:
[tex] \sqrt{105} [/tex]
Step-by-step explanation:
Using the geometric nean theorem, if we let the hypotenuse be x, then:
[tex] \frac{7}{x} = \frac{x}{15} [/tex]
[tex] {x}^{2} = 105[/tex]
[tex]x = \sqrt{105} [/tex]