Final answer:
The constant percent rate of change for y = 4.2x is 4.2%.
Step-by-step explanation:
The constant percent rate of change is a concept used in mathematics to describe the rate at which one quantity changes in relation to another quantity. In the equation y = 4.2x, the constant percent rate of change is 4.2%. This means that for every 1 unit increase in the independent variable x, the dependent variable y increases by 4.2 units.