Since the decay rate is constant for each day we can consider it as a slope and represent it as a linear function that fits the population decay.
![y=mx+b](https://img.qammunity.org/2023/formulas/mathematics/high-school/smsb8cbft03lwblmi49nf2l6jby2ofxzws.png)
since it is a decay we know that the slope is going to be negative and b is going to be the initial population.
![y=-25x+1640](https://img.qammunity.org/2023/formulas/mathematics/college/tvtdzjnnnb2k7nkcskkaqmgh0kvxler7s3.png)