Each student needs 4 stencils and 6 colored pencils for a project. if a class uses 27 colored pencils for the project, how many stencils do they used?

If the class used 27 colored pencils, that means 4 students had six pencils and four stencils. That means there is a fifth student that only had three colored pencils. If it follows the rule the student most likely only had two stencils. If this was the case then the class used 18 stencils. 

I’m pretty sure the slope would be 1 since the x and y values increase by 1