Following a certain logic, $15$ is related to $45$. Following the same logic, $25$ is related to $125$. Using the same logic, which of the following numbers is related to $80$?

Let's analyze the pattern between the numbers:
The relationship followed is:

$$\text{First Number}\times \frac{\text{First Number}}{5}=\text{Second Number}$$

$$⟹\frac{x^2}{5}=y$$

Let's verify with the given pairs:

1. For $15\to 45$:

$$\frac{15^2}{5}=\frac{225}{5}=45$$

2. For $25\to 125$:

$$\frac{25^2}{5}=\frac{625}{5}=125$$

Now, applying the same logic to find the number $x$ related to $80$:

$$\frac{x^2}{5}=80$$

$$x^2=80\times 5$$

$$x^2=400$$

$$x=\sqrt{400}=20$$

Therefore, $20$ is related to $80$.