The seventh- and eighth-grade students at a school voted on whether to have a picnic for a year-end activity. The results showed that 75% of the seventh-grade students and 45% of the eighth-grade students voted for a picnic. In addition, 30 more seventh-grade students than eighth-grade students voted for the picnic. Let represent the total number of seventh-grade students and y represents the total number of eighth-grade student. Which equation represents the relationship between the number of seventh-grade students and the number of eighth-grade students at the school?