To solve these equations, we will simplify and isolate the variable x.

3. (x+4) - 128 = 23
First, we will combine like terms on the left side of the equation:
x + 4 - 128 = 23
x - 124 = 23
Next, we will isolate the variable x by adding 124 to both sides of the equation:
x - 124 + 124 = 23 + 124
x = 147

So the solution to the equation is x = 147.

12. (x-17) - 125 + (-89)
First, we will combine like terms on the left side of the equation:
x - 17 - 125 - 89
x - 231
So the simplified equation is x - 231.

7. (x-5) - 100 + (-58)
First, we will combine like terms on the left side of the equation:
x - 5 - 100 - 58
x - 163
So the simplified equation is x - 163.