how to set up a proportion with this info
There were 30 campers in Crazy Creek Park on Saturday when it started to rain. In the first hour of rain, 3 campers took down their tents and went away. In the second hour, 6 campers took down their tents and left the park. The rain kept pouring down. Every hour 3 more campers left than during the hour before. In what hour did the last campers leave the park?