The Aoki family and the Hill family each used their sprinklers last summer. The water output rate for the Aoki family's sprinkler was 30 L per hour. The water output rate for the Hill family's sprinkler was 20 L per hour. The families used their sprinklers for
a combined total of 40 hours, resulting in a total water output of 950 L. How long was each sprinkler used?