What’s the length of this missing leg?

Answer:
b = 4.5 mm
Step-by-step explanation:
using Pythagoras theorem:
a² + b² = c²
4² + b² = 6²
b² = 6² - 4²
b² = 36 - 16
b² = 20
b = √20
b = 4.5
Pythagoras theorem:
a² + b² = c²
4² + b² = 6²
b² = 6² - 4²
b² = 36 - 16
b² = 20
b = [tex] \sqrt{20}[/tex]
b = 4.5