The Ramirez family and the Bennett family each used their sprinklers last summer. The water output rate for the Ramirez family's sprinkler was 35 L per hour. The water output rate for the Bennett family's sprinkler was 40L per hour. The families used their sprinklers for a combined total of 55 hours, resulting in a total water output of 2100 L. How long was each sprinkler used?