For dogs that are two or more years old, the equation $\displaystyle 5x-y+12=0$ compares dog year to human years. In the equation, $\displaystyle x$ represents the acutal age of a dog, and $\displaystyle y$ in the age of the dog in human years.

What rate of change does the slope represent?

Testbook answer: 5 dog years for every human year.

I don't why though? Can anyone help me out? Thanks.