How do i find the y value for point i such that di and ei form a 3: 5 ratio.

d=(-3,2)
e=(5,5)

3:5 ratio mean there are 8 "parts" (3 + 5 = 8)

The distance between the x-coordinates is |-3 - 5| = 8.
So each "part" is 8/8 = 1 unit long in the x-direction. 
You want I to be 3(1) = 3 units from D, so the x-coordinate of I is -3 + 3 = 0.

Same deal for y.
|2 - 5| = 3 is the distance between D and E
Each part is 3/8.
3(3/8) = 9/8
2 + 9/8 = 25/8

So the point I is (0, 25/8)