Dilatation is the transformation that produces and image that is the same shape as the original, but different size. So, in order to find the dilatation of a triangle, you need to multiplícate by a scale factor the given coordinates. An ex: A'(0,2), B'(2,-1), and C'(-2,-2) , lets say that you are going to múltiple by 2, the formula would be (2x, 2y), and the results will be A'(0,4) B'(4,-2), C' (-4,-4).
You should be able to multiply 91 by 8 to get the sum of the first 8 tests, then add the score on the 9th test. Then to get the average of the sum of the 9 tests you need to divide it by 9. ((91*8)+78)/9=89.555555555555.... So, 90%
