there are 13 students in Sara's class. I did this by using 8 = 3/5x, x being the total number of students. The answer is 13.33334 but you cant have half a student so it rounds down to 13.
also number 4 can be any positive number. This is because if you take one fourth of a negative number it will be more than if you doubled it. for example 1/4 of -4 is -1 which is more than -4 doubled which is -8