In order to compare the performances of candidates in two schools a test was given. The mean mark at school A was 45, and the mean mark at school B was 31 with a standard deviation of S. The marks of school A are scaled so that the mean and standard deviation are the i same as school B and a mark of 85 at school A becomes 63. Find the values of a and b if the transformation used is y-ax +

b. Find also the original standard deviation of the marks from school A.