Answer
$144$
Work Step by Step
Substituting $
S=15
$ in the given equation, $
S=2\sqrt{I}-9
,$ results to
\begin{array}{l}\require{cancel}
15=2\sqrt{I}-9
\\
15+9=2\sqrt{I}
\\
24=2\sqrt{I}
\\
\dfrac{24}{2}=\sqrt{I}
\\
12=\sqrt{I}
.\end{array}
Squaring both sides, the equation above is equivalent to
\begin{array}{l}\require{cancel}
(12)^2=\left( \sqrt{I} \right)^2
\\
144=I
.\end{array}
Hence, the IQ score, $I,$ is $
144
.$
