In this case, we'll have to carry out several steps to find the solution.
Step 01:
Data
BC = 20 mm
DF = 30 mm
AB = x
KL = 4 mm
KJ = 8 mm
MN = y
Step 02:
We must apply properties of similar figures.


4 * 30 = 20 * y
120 = 20y
120/20 = y
6 = y


4 * x = 8 * 20
4x = 160
x = 160 / 4
x = 40
The answer is:
x = 40 mm , y = 6 mm