Answer:
b = 6 mm
Step-by-step explanation:
Using Pythagoras' identity on the right triangle.
The square on the hypotenuse is equal to the sum of the squares on the other 2 sides, that is
b² + 8² = 10²
b² + 64 = 100 ( subtract 64 from both sides )
b² = 36 ( take the square root of both sides )
b = = 6