20
Start with

Multiply both sides by 4:

Subtract 40 from both sides:

21
If the absolute value of something equals 12, then that something is either 12 or -12: the possibilities are

or

22
You can isolate the absolute value

And proceed as before.
23
Distribute the 16:

24
Multiply both sides by 6/5:

25
Start with

Subtract 32 from both sides

Multiply both sides by 5/9
