Some situations can be represented by a linear equation.

Linear equations have a constant rate of change.

In a linear equation of the form *y* = *mx* + *b*, *m* is the rate

of change or slope, and *b* is the initial value or *y*-intercept.

First, find the rate of change. Parking costs $1.50 for each additional hour, so the rate of change is $1.50 per hour.

Next, find the initial value. The airport charges $2 for the first hour of parking, so the initial value is $2.

Write an equation where

*m* = 1.5 and

*b* = 2.

*y* = 1.5*x* + 2

In this situation, the slope, or rate of change, is 2.75, and the

*y*-intercept, or initial value, is 10.

The rate of change is multiplied by the distance, *x*, to find the cost.

So, the slope represents the cost per mile, which is $2.75 per mile.

The initial value is the cost before the letter is carried any distance.

So, the *y*-intercept represents the service fee, which is $10.