​ Evaluate!!!

I have no Idea of what to do.

I need help fast!!!

Hi, in this type of questions we always follow these steps:

Step 1: let the a variable be equal to this expression.

For instance,

$x=\sqrt{12+\sqrt{12+...}}$

Step 2: Square both sides:

$x^2=12+\sqrt{12+...}$

But, notice, x was defined to be these "squareroots" right?

So: $x^2=12+x$

Step 3: We solve this equation.

$x^2=12+x \\ \iff x^2-x-12=0 \\ \iff (x-4)(x+3)=0\\ \iff x=4 \\ \text{Note: We rejected x=-3 as we know x>0 (as the squareroot of any number is non-negative)}$

$\mbox{draw[blue, very thick] (0,0) rectangle (3,2)}$Thanks, now I get it. 

Well the next promblem is

  $\sqrt{12-\!\sqrt{12-\!\sqrt{12-\cdots}}}$

It's the opposite if this promblem

The promblem is $\sqrt{12-\!\sqrt{12-\!\sqrt{12-\cdots}}}$

Thanks, I think I might be able to solve the next promblem.