your grade in Class varies directly with how many hours you study. you study for 3 hours and get a 60. What grade would you get studying 4.5 hours

To do this question you can use proportions.

3/60 is simplified to 1/20.

This shows that if you study 1 hour you get a 20. So to find the answer you multiply each side by 4.5, this means that if you study 4.5 hours you get a 90.