How do systems of non-linear equations represent “real life” situations?

An example of system utilization of not linear equations in the daily life is the employment of quadratic equations. Across the same ones, the carpenters and other professionals use them to optimize the area of a space with perimeter and certain dimensions. For example in real life we could have an example of a room, which measures, the length should be 2 meters bigger than his width. This might be represented across the following equation of the second degree

A=W*(W+2) =W*W+2*W

answer: do you still need this?