Answer
$b=24$
Work Step by Step
In the given right triangle, $a$ and $b$ are the legs and $c$ is the hypotenuse. Using $a^2+b^2=c^2$ or the Pythagorean Theorem, with $
a=7
$ and $
c=25
,$ then
\begin{array}{l}\require{cancel}
a^2+b^2=c^2
\\\\
7^2+b^2=25^2
\\\\
49+b^2=625
\\\\
b^2=625-49
\\\\
b^2=576
\\\\
b=\sqrt{576}
\\\\
b=24
.\end{array}