Let the class period be x
10% of x is
[tex]=\frac{10}{100}\times x=0.1x[/tex]If the remaining time is 45 minutes, i.e
[tex]x-0.x=45[/tex]Solve for x to find the class period
[tex]\begin{gathered} x-0.x=45 \\ 0.9x=45 \\ \text{Divide both sides by 0.9} \\ \frac{0.9x}{0.9}=\frac{45}{0.9} \\ x=50\min \end{gathered}[/tex]Hence, the class period, x, is 50 minutes
