Before the storm, there were already 6 inches of rain on the ground, and after the storm, there were 33 inches of rain on the ground. If it
rained at a constant rate during the storm, and if the storm lasted for 9
hours, find the equation of the function that represent the number of
hours since the storm started. Let x represent the number of hours
since the storm started and let y represent the number of inches of
rain on the ground.