The Solution.
Step 1:
We shall represent the problem in a diagram.
Step 2:
We shall use Similarity Theorem to find the height of the flagpole.
Let H = height of the flagpole.
[tex]\begin{gathered} By\text{ Similarity,} \\ \frac{AB}{AC}=\frac{AD}{AT} \\ \\ \frac{4}{30}=\frac{6}{H} \\ \text{Cross multiplying, we get} \\ 4H=30\times6 \\ 4H=180 \\ \text{Dividing both sides by 4, we get} \\ H=\frac{180}{4}=45\text{ feet} \end{gathered}[/tex]Thus, the correct answer is 45 feet.