Describe a real world situation where the relationship is linear and nonproportional

Supposed sally always pay a tip of 10$ whenever she goes out for dinner.
Thus,
Total spending =cost of food+10$
This is non proportional because if we plot this on graph it will never pass through origin (0,0)

We can separate linear equations into two categories: proportional and non-proportional relationships. A linear equation y = mx + b:

There is a proportional linear relationship between y and x if b = 0 (so y = mx),
There is a non-proportional linear relationship between y and x if b ≠ 0.

Because the price would be 25% off the 25% off, which for example would be 25% off 20 dollars, which it would be 15 dollars. then, 20% off 15 dollars would be 11.25, and not 10.