Answer:
4
Explanation:
The figure can be split into 2 triangles, the larger one is the whole figure with base 18 and height 9. while the other small triangle has base 8 and height h. Since they are both right angled triangles with a shared angle, they are similar.
With similar triangles, we get the ratio of base : height = 8 : 8+10 = h : 9
Hence, 8 : 18 can be simplified to 4 : 9, which is also equal to h : 9. From here, we get h = 4.