Hi!
I believe that the answer is C. proportional ; $50 per month , because there is a pattern . You just keep adding 50 , if you don't know how to find the unit rate just find the difference between 100 and 50 , in other words 100 minus 50 , which equals to 50 .
1 month - 50
2 months-100
3 months-150
4 months-200
5 months-250
6 months-300
7 months-350
8 months-400
Hope it helps and have a wonderful day!