y = 3x (cost of apples at $3 each)
Sara sells apples for three dollars each. Let's graph how the total cost grows as she sells more.
Here's a table to track apples sold and the cost.
One apple is three dollars. Two apples is six. Three apples is nine.
Now let's graph it. Draw two number lines that meet at zero — the origin.
The bottom axis counts apples. The side axis shows the cost in dollars.
One apple, three dollars. Plot the point one comma three.
Two apples, six dollars. Plot two comma six.
Three apples, nine dollars. Plot three comma nine.
All three points line up! Connect them with a straight line.
And look — the line passes right through the origin, the point zero comma zero.
For every one more apple, the cost climbs by three dollars. That's our unit rate.
A straight line through the origin shows a proportional relationship. Here, y equals three x.