Expand the Brackets

5d(2 - 3d) → 5d*2 - 5d*3d → 10d - 15d²

Would it be 

5d2 - 5d3d

or 

10d - 15d

???

oh ok so the second one but there are two d so d²

... there are two d so d² 

Yes, but be clear that when you say "two d" you mean d*d not 2d.

No. Look at what Alan did:

He multiplied 5d(outside the bracket) by 2(inside the bracket), like this:

5d X 2=10d, that's the first term.

Then he mutiplied 5d by the second term inside the bracket(3d) like this:

5d X 3d=15d^2. All he did was to multiply 5 X 3=15 and then d X d =d^2.

Then you just put them together:15d^2. Remember this means: 15 X d^2.

So the whole expression becomes: 10d - 15d^2