I don't get how to get N, please show me cause I don't understand

You follow the math.

k = 0.693/t1/2
Then
ln(No/N) = kt
No = 120 ug
N = solve for this
k = from above
t = 120 sec.

First, you substitute the half life of this material which is listed as 20 seconds and that allows you to solve for k. You need k to solve the equation below it in the solution above.
Then you substitute 120 ug for No (No is what you have at the beginning). N is what you have at the end and that is what you're solving for. N is the only unknown in the equation. Then substitute k from the first calculation above. t in the problem is 2 minutes but since the half life was given in seconds this 2 min need to be convert to seconds which is 120 s. So the final equation looks like this
ln(120/N) = k(120). I don't remember k but that is what you obtained from above. Solve for N.

Um so is it like this :

0.693 x 120 = 83.16
120/n=83.16
=9979.2?

No, you aren't following the math.

The half life is 20 seconds.
k = 0.693/t1/2 = 0.693/20 = 0.03465.
Then ln(120 ug/N) = 0.03465*120
Solve for N.
By the way, that ln (which you don't have anywhere in your work) in front of the (No/N) is not for looks. That means to take the natural log (that's the log base e) of No/N.

Alright, my final answer is 166.32

is this correct?

No. If the sample starts out at 125 ug and it loses half of the sample every 20 seconds, how can it have more than it started with at the end of 2 minutes. It MUST be less than 125 ug.

Yah that's wut I thought so I tried again and I know I sound dumb but is it .0115 ?

K this was my equation 120in/n=1.386

How do I solve for n?

Much closer but not quite.

I think part of the problem is the 1.386. I think that should be 4.158.
k = 0.693/20 = 0.03465
ln(125/N) = 0.3465*120
ln(125/N) = 4.158
Take the antilog of both sides.
antilog ln(125/N) = 125/N
antilog 4.158 = 63.94
So 125/N = 63.94
and N = 125/63.94 = 1.95 ug

Oh now I get it! Thank u so much for ur help:)

To help you understand how to get N, could you please provide some more context or specify what N refers to? This will allow me to guide you through the process more accurately.