Tara takes her pulse in order to determine her resting heart rate, measured in beats per minute ( bpm ) (bpm)left parenthesis, start text, b, p, m, end text, right parenthesis. She takes it for three minutes, and makes the following chart of the results. We'll assume that Tara's heart rate is constant over the three-minute period.

Let x represent the number of minutes.

Lets y represents the number of beats.

Now consider the graph, when the time is equal to 1 min, the total beats are 60. We can say that this point can be taken in a coordinate plane as (1,60).

Similarly, when time is equal to 2 mins, total beats are 120, and when time is equal to 3 mins, total beats are equal to 180 mins. So the these points on the coordinate plane can be represented as (2,120) and (3,180)

Plot all the three points, and draw a line which joins them and extend the line. The line shows the proportionality relation between both values