Emilia loves to play the piano but doesn't like practicing the exercises her piano teacher assigns. Emilia knows the exercises will help her play better though, so she tries to motivate herself using her favorite treat — chocolate chip cookies. There is a proportional relationship between the amount of time (in hours) that Emilia practices the piano, x, and how many cookies she gives herself, y.
When Emilia practices for 1 hour, she gives herself 4 cookies. Write the equation for the relationship between x and y.