The first four coefficients in the general expansion are:
1, 7, 21, 35.
These coefficients combine with the variables:
(3c)⁷, (3c)⁶(4d), (3c)⁵(4d)², (3c)⁴(4d)³
So the fourth variable component is (81)(64)c⁴d³ and the whole term is:
(35)(81)(64)c⁴d³=181440c⁴d³.