Pascal's triangle to expand the binomial (d − 5 y) ^6?

The pascal triangle for the expansion of a binomial expression of to the 6th power is given by:

                                                 1
                                              1     1
                                           1     2    1
                                        1    3     3    1
                                     1    4    6     4    1
                                  1    5   10  10    5    1
                               1    6   15  20   15   6    1

Thus, the expansion of is given by:

The answer is: y would equal 3 because if you simplify the equation then it would be y= 3x+9 and if you divide 3x and 9 by 3 it would equal 3. y= 3