The values of the missing sides in each system of two similar triangles are: Case 3: x = 4.8, Case 4: x = 14.482, Case 5: x = 18.462, Case 6: x = 11.372.
How to determine the value of a missing side associated with a system of two similar triangles
In this problem we find four cases of pairs of similar triangles, that is two triangles with similar angles and proportional sides. Each case can be defined by proportion formulae.
The result for each case is shown below:
Case 3:

x = 4.8
Case 4:

x = 14.482
Case 5:

x = 18.462
Case 6:

x = 11.372