I need help with this geometry question, thanks!
The shaded area in the diagram below shows the cross section of a square pyramid intersected by a plane parallel to the base. The pyramids edges are all 15 cm long.

A pyramid with a square base of side 15 cm is shown with a shaded cross section parallel to the base and meeting an edge at a point 5 cm above the base and 10 cm below the apex.

What is the perimeter of the shaded area?

Question

I need help with this geometry question, thanks! 
The shaded area in the diagram below shows the cross section of a square pyramid intersected by a plane parallel to the base. The pyramids edges are all 15 cm long.
 
A pyramid with a square base of side 15 cm is shown with a shaded cross section parallel to the base and meeting an edge at a point 5 cm above the base and 10 cm below the apex.
 
What is the perimeter of the shaded area?

anonymous · Answer

http://learn.flvs.net/webdav/assessment_images/educator_geometry_v14/pool_Geom_3641_0709_28/image0034e613130.jpg

campbell_st · Answer

well if you use the ratio of original to smaller

edge length of the original is 15cm  edge length of the smaller is 10cm   

the same ratio will apply to base edges.. 

$$\frac{10}{15} = \frac{x}{15}$$

as you can see the length of the base will be 10 cm

anonymous · Answer

Thank you so much, i get it now.