Answer:
The equation represents a relationship between the variables y and x. Specifically, if x is viewed as a measure of time (say, in seconds), then for any given value of time x, Alonso's walking speed (y) will be three times that value.
The point (3, 9) represents a relationship between a value of time (3), and Alonso's walking speed at that time (9, which is ).
The point (5, 15) also represents a relationship between a value of time (5), and Alonso's walking speed at that time (15, which is ).
Step-by-step explanation:
The variable x could be seen as a measure of anything (time, distance, etc.), but what matters here is that there is a relationship between two numbers x and y. Specifically, y is three times whatever number x is. This means that given any x value, we can find out what y is.
There's other observations we can make about the graph, but I wasn't sure about the level of the question here. We could say the graph is one to one (y as a function of x has exactly one inverse, and therefore the relationship between x and y is bijective, assuming x and y are real numbers). We could say the graph is always increasing since dy/dx = 3 (given a value of x, the rate of instantaneous change is 3) (aka the slope is 3).