Answer :
[tex]x-minutes\ in\ school\\15\%=0.15\\100\%=1\\\\From\ proportion:\\\\75\ \ \ -\ \ \ 0.15\\x\ \ \ \ \ -\ \ \ 1\\\\0.15x=75\ \ \ |:0.15\\x=500\\\\He\ spends\ 500\ minutes\ in\ school.[/tex]
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
[tex]\Rightarrow x\times \dfrac{15}{100}=75[/tex]
[tex]\Rightarrow x=75\times \dfrac{100}{15}[/tex]
[tex]\Rightarrow x=\dfrac{7500}{15}[/tex]
[tex]\Rightarrow x=500\ \text{minutes}[/tex]
[tex]\Rightarrow x=\dfrac{500}{60}\ \text{hours}[/tex]
[tex]\Rightarrow x=\dfrac{25}{3}\ \text{hours}[/tex]
[tex]\Rightarrow x=8\dfrac{1}{3}\ \text{hours}[/tex]
Therefore, Kai spends 8 hours 20 minutes in school.