Thank you for the opportunity to help you with your question!

Given that the figures are similar, this means that the length of the corresponding sides increase proportionally hence the proportion between the second figure and the first figure is:-

We use the known values two corresponding sides, hence = 6/4

Therefore Z= 6/4 *8 =12

Y=4/6*20 =13.3

X= 4/6*18 =12

Please let me know if you need any clarification. I'm always happy to answer your questions.