You need to know these two formulas:

For example,

First write the equation 8 + 12 > x because according to the triangle property, the sum of any 2 sides have to be greater than the third side. This means that the difference of any two sides should be smaller than the third side.
So, the answer would be 4 < x < 20.
| -2.3 | = 2.3
the absolute value of any number is positive, even if it says negative
1,000:) is going to be your anwser!