How to solve a quadratic equation by taking square roots?

I'm bad at explaining things, so I will show you an example.

Equation: 4t² = 25
1). Take the square root of both terms

√4t² = √25

√4t² = 4t 
√25 = 5 (5x5 = 25)

Now, you are left with 4t = 5
Divide each side of that equation by 4

    4t = 5
   
    4     4
 
 t = 5/4 or -5/4

I don't know why, but the answer can be positive or negative. I'm still trying to understand that :)

I hope that this helps you a little bit!

The answer is, the streetlight is 18 inches tall.