Answer:
The error of his estimate was $25.
Explanation:
The error of an estimate is given by the estimated value subtracted by the real one. Since John estimated that he would spend $100 and he only spent $75 than the error of his estimate is:
![\text{error} = 100 - 75\\\text{error} = 25](https://img.qammunity.org/2021/formulas/mathematics/high-school/harisjvxq0lpswj6h7sz57yimtxmwp9td7.png)
The error of his estimate was $25.