Why can't the 4 be taken out of the abs value markers??

[broken hemlock]

wouldn't you just add the 4 to the to 5 and make 9?

[maiden seal]

You can't take addition or subtraction out of absolute value bars because imagine if 3x is positive, then subtracting 4 will make the absolute value smaller
but if 3x is negative, subtracting 4 will make the absolute value larger

if you take the 4 out of the absolute value bars, it won't behave the same

[safe trellis]

No you can't directly take out as it's a modulus function so it has 2 way of opening up

[broken hemlock]

So let's say there was no 15d, then you could take the 4 an add it it to the 5? So it's basically just because there's a variable

[maiden seal]

if there were no variable, and it was just $|-4| + 5$, you'd take the absolute value of -4, which is 4 \
$|-4| + 5 = 4 + 5 = 9$