when u=-2, put that in where you see "u". use parentheses.
-4(-2)+4x=12
-4*-2=8 ➡positive 8 since a negative times a negative is always positive
一一一一一
now look for x
8+4x=12
subtract 8 from both sides. get x by itself.
-8+8+4x=12-8
4x=4➡ divide both sides by 4. a number divided by itself is 1 (unless one side is negative, then the answer is negative)
4/4=1
一一一一一
x=1