Martha recorded the ratio of students and teachers at all the middle schools in the Timber Creek school district. The list is shown below. 20 students : 2 teachers 1 teacher per 15 students 1 teacher per 10 students 40 students : 4 teachers 5 teachers per 40 students Part A: Identify the unit rates and ratios that are equivalent. Part B: Give another unit rate or ratio that is not on the list but is equivalent to the ones from Part A. Explain why these are equivalent.