Answer
b=40
Work Step by Step
Use the Pythagorean Theorem to find the missing length.
$a^2+b^2=c^2\longrightarrow$ substitute the given values
$9^2+b^2=41^2\longrightarrow$ simplify exponents
$81+b^2=1681\longrightarrow$ subtract 196 from each side
$81+b^2-81=1681-81\longrightarrow$ subtract
$b^2=1600\longrightarrow$ find the square root of each side
$\sqrt{b^2}=\sqrt{1600}\longrightarrow$ simplify
$b=40$
