find the missing height in the diagram.

Explanation:

Step1: Analyze vertical lengths

The total vertical length is 12 ft. The part of the vertical length of the upper - part of the figure is 8 ft.

Step2: Calculate missing height

We find the missing height by subtracting the known vertical length from the total vertical length. Let the missing height be $h$. Then $h = 12 - 8$. $h=4$

Answer:

4