Since we want the percentage that he saved, we have to identify the amount it saved and the total initial amount.
Since the amount reduced from $90 to $75, the initial amount was $90 and the reduction was a total of:
![90-75=15](https://img.qammunity.org/2023/formulas/mathematics/college/7798uhuyc6wtcaakbvoi0d5eizcj8gwbwj.png)
Thus, the percentage is the ratio between the reduction and the total:
![(15)/(90)=0.1666\ldots\approx0.1667=16.67\%](https://img.qammunity.org/2023/formulas/mathematics/college/syjnnhz3sjcd62d4ax5db2zwdxsetvhoub.png)
So, the amount he saved is approximately 16.67%.