Answer
b = 15
Work Step by Step
We will use given data about triangle ABC & Pythagoras Theorem to solve for 'b'-
We know that -
$c^{2} =a^{2} + b^{2}$ ( Pythagoras Theorem)
Therefore -
$b^{2} =c^{2} - a^{2}$
$b^{2} = (17)^{2} - (8)^{2}$
$b^{2} = 289 - 64$
$b^{2} = 225$
therefore $ b = \sqrt (225)$
b = 15
