Always true because there are no other options that allow the equations to be true
a = 4
Can you add anything else to 4 to get 8? No.
4 - m = 2
-m = -2
m = 2
Can you subtract anything besides 2 from 4 to get 2? No.
So the statements are always true.
The equation can be described as a single linear equation in one variable with the variable on only one side of the equal sign and having a non-zero coefficient. Such an equation will always have exactly one solution. The solution can be found by simplifying the equation to the form ...
x = a
where x represents the variable, and "a" represents an appropriate constant, found by using the properties of arithmetic and equality.