Line division question, pretty certain on the first answer but cant get the right one to the second drop down

Let me first check on your first answer.

AB is divided in a ratio of 3:2.
3 + 2 = 5, so point C is 3/5 of the way from A to B and 2/5 of the way from B to A.

Work on x-coordinate of point B.
3.6 - (-6) = 9.6
3/5 * 9.6 = 3.2
5 * 3.2 = 16
16 + (-6) = 10
x-coordinate of A is 10

Work on y-coordinate of point B.
5 - (-0.4) = 5.4
5.4/3 = 1.8
1.8 * 5 = 9
5 - 9 = -4

Good job!

Now onto point D.

D is in a 4:5 ratio from C to B.
4 + 9 = 9, so C is 4/9 of the way from C to B.

Work on x-coordinate of D
10 - 3.6 = 6.4
6.4/9 = 6.4/9
3.6 + 4 * 6.4/9 = 32.4/9 + 25.6/9 = 58/9

Work on y-coordinate of D.
-4 - (-0.4) = 3.6
3.6/9 = 0.4
-0.4 - 4 * 0.4 = -0.4 - 1.6 = -2

D(58/9, -2)

Maybe the answer is 20mm. all i really did was just multiply, which is obvious.