Relationship of the form y = kx + b where k ≠ 0 and b ≠ 0.
Example
The cost of a taxi ride includes a base cost plus another cost related to the distance travelled by the taxi.
If the base cost b is $8 and if the cost x per kilometre travelled is $1.50, the following relationship determines the total cost y : y = 1.50x + 6.