Answer-
Kai spends 8 hours 20 minutes in school.
Solution-
Let us assume, Kai spends x minutes in school.
Kai calculates that he spends 15% of a school day in science class and that is 75 minutes, i.e
\Rightarrow x\times \dfrac{15}{100}=75⇒x×
100
15
=75
\Rightarrow x=75\times \dfrac{100}{15}⇒x=75×
15
100
\Rightarrow x=\dfrac{7500}{15}⇒x=
15
7500
\Rightarrow x=500\ \text{minutes}⇒x=500 minutes
\Rightarrow x=\dfrac{500}{60}\ \text{hours}⇒x=
60
500
hours
\Rightarrow x=\dfrac{25}{3}\ \text{hours}⇒x=
3
25
hours
\Rightarrow x=8\dfrac{1}{3}\ \text{hours}⇒x=8
3
1
hours
Therefore, Kai spends 8 hours 20 minutes in school.