Answer:
x = 7 cm
Explanation:
The same-measure angles tell you the vertical lines are parallel, so the crossing segments between them are divided into the same proportion. That is, ...
... x/(42 cm) = (6 cm)/(36 cm)
... x = (42 cm) · 6/36 . . . . multiply by 42 cm
... x = 7 cm . . . . . . . . . . . . simplify