To do this we use FOIL method, this method calls for 2 parenthesis and 4 expressions, which is what we have here, how FOIL works is (multiplying):
First with first
Outer with outer
Inner with inner
Last with last
So always follow this method when you have a situation like this so,
F: 4d² (d * 4d)
O: -3d
I: 8d
L: - 6
So the full expression would be: 4d² - 3d + 8d - 6
If you have any question, please ask me, good luck!