If the equation y=mx+b is used to model a quantity y as a function of the quantity x, why is b considered to be the starting value?

This is because even when the quality of the variable x is 0, the value of b still exists and is the starting point for y.

Step-by-step explanation:

To prove this, we start with the base form of the equation and input 0 for x.

y = mx + b

y = m(0) + b

y = 0 + b

y = b