As part of a new fitness plan, Sabir runs on a treadmill at the same speed for 15 minutes every morning. The table shows the calories he burns over time.

Time (in minutes) Number of calories
Burned

3 15
6 30
9 45
12 60

Write an equation to represent the relationship between the time Sabir runs and the number of calories he burns. Use x as the independent variable and y as the dependent variable.