The otiginal price will be the 100% and the sale price will be the 100% minus the 30% so will be the 70%, so with this information we can use a rule of 3 to solve the problem so:
[tex]\begin{gathered} x\to100 \\ 15.75\to70 \end{gathered}[/tex]so the equation will be:
[tex]\begin{gathered} x=\frac{100\cdot15.75}{70} \\ x=22.5 \end{gathered}[/tex]