I need help please.

Answer:
b = 3[tex]\sqrt{10}[/tex]
Step-by-step explanation:
Since the triangle is right use Pythagoras' identity to solve for b
The square on the hypotenuse is equal to the sum of the squares on the other two sides, that is
a² + b² = c², substitute values
([tex]\sqrt{10}[/tex] )² + b² = 10²
10 + b² = 100 ( subtract 10 from both sides )
b² = 90 ( take the square root of both sides )
b = [tex]\sqrt{90}[/tex] = [tex]\sqrt{9}[/tex] × [tex]\sqrt{10}[/tex] = 3[tex]\sqrt{10}[/tex]