Don't understand this Integral step

[hexed wing]

Where the blue arrow is pointing to, I rlly just don't understand this whole step. Like how did they remove the abs value brackets, how they used u-sub, and how 4 was multiplied out of the integral?

[brazen marsh]

The graph of |sin(4t)| contains 4 identical "hills" between 0 and π. The first and third correspond to sin(4t), the second and fourth - to -sin(4t).
So, we can integrate over just one "hill" and multiply the result by 4.

[hexed wing]

Ahhhh I get it

But how did the upper limit of pi turn into pi/4?

[brazen marsh]

Well, as I said, we have 4 hills between 0 and π.

So, the first hill is between 0 and π/4.

[hexed wing]

Oh ok

Ty!!