A function can be defined in the following six ways:
1. By a verbal rule: Total cost of roses when the unit price is $3. 
2. As an equation: y = 3x. 
3. As a set of points: (0, 0), (1, 3), (2, 6), (3,9). 

5. As a diagram:  6. As a graph: 
CONCEPT CHECK: Out of the 6 representations, the one showing the best that the function's values are increasing is representation number: