You didn't supply a list. The so-called rigid transformations of translation, rotation and reflection create congruent triangles.
Generally it's dilation by a factor about a point is preserves similarity but not congruency. Any transformation which includes such scalings but is otherwise rigid also preserves similarity but not congruency.
So this is what i did but im not sure if its 100% correct
585 / 9 to get the number of groups = 65
then you take 65 x 3 for number of students in each group and you get the final answer of 195 students
-12x^6 - 60x^5-75x^4.......GCF = 3x^4
3x^4(-4x^2 - 20x - 25)
3x^4(-2x - 5)(2x + 5) <==
