Can someone help me please 

Wow !  If I understand what's go0ing on here, then
we have to be careful, and THINK .

I was going to ask you "What does  Ф  mean ?", and then I realized,
Ф is a new operation that the teacher invented.

The first line on the board is the definition of Ф .

Ф means "Add the two numbers and subtract 4."

Now you have to use this new invention to find the value
of the second line:

Take care of the stuff inside the parentheses first: ( 4 Ф 2 )
Add the two numbers and subtract 4
4 + 2 - 4 = 2
That's the part inside the parentheses. It's 2 .

NOW, we have to do the new operation with the 2 inside,
and the 3 that's outside the parentheses:

3 Ф 2
Add the two numbers and subtract 4
3 + 2 - 4 = 1

And that's the final value of 3 Ф (4 Ф 2) .  It's 1 .

Pretty sneaky.