Answer:
v = 25
Step-by-step explanation:
The crucial information you need to know to solve this is to realize that HI and GH are the same length. However, why they are equal is not immediately obvious.
Both sides of the middle line (HF) are symmetrical, since G and I are the same distance away from the line, and they both lie on a line perpendicular to the middle line.
Note: we know they're the same distance away due to the small red marks in the lines, indicating that they're the same length.
The angles at G and I in the triangles are also the same, as the lines from G and I both meet at H. If they were different angles, they would each hit a different point on the middle line.
Thus, we can conclude that GH and HI are the same length.
Since we know the following:
GH = 4v - 75
HI = v
We can set GH and HI equal to each other and solve the equation.
4v - 75 = v
Subtract v from both sides:
3v - 75 = 0
Add 75 to both sides:
3v = 75
Divide both sides by 3:
v = 25
Answer: v = 25
ft tall and the finished stack of bricks is 
ft tall.