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!
I know that the diameter is double of the radius, so I can divide 6 by 2 to get 3. 3.14(3)^2 gives me 28.26.