Question 730438
You could use a lattice method.  It is essentially the same as either the "horizontal" or the "vertical" way of multiplying.  Arrange the terms such that one polynomial forms a row (top) and the other forms a column (along a side).  Now you fill in the grid spaces with each partial multiplication.  THOSE will be the terms to add and possibly from which to simplify the resulting sum.


Hard to show in this site system but something like this:

_______-d^2__________4d___________3

3d^2

-7d

6


You will have nine grid locations to fill.  



_________-d^2__________4d___________3

3d^2_____-3d^4_________12d^3_______9d^2

-7d_____7d^3___________-28d^2______-21d

6_______-6d^2_________24d_________18


This lattice arrangement makes finding which like-terms to combine easy to do.  Notice where the d^2 terms are located.  Notice where the d^3 terms are located. (Not the ones in the main row and column; the ones in the interior locations.)