Hey there!
In order to factorise an expression, we need to factor out the greatest common factor (divide all the terms in the expression by the greatest common factor):
6ac-4ad
In this case, the greatest common factor is 2a.
Put it outside the parentheses:
2(3c-2d)
That's the answer.
Hope everything is clear.
Let me know if you have any questions!
#LearningDoesn'tEnd
:-)