Like terms are defined as terms with the same variables that are raised to the same power.
For example, the terms ax and are NOT like terms because the coefficients a and b have variables (x and , respectively) that are not raised to the same power.
In the expression , the like terms are grouped as follows:
-3x (this is negative because the subtraction sign is "distributed" to the terms inside of the parentheses)
4, -7, -1 (the reason for why it's -7 is the same reason for why -3x is negative)
Add the terms in the groups up...
Now you have the simplified expression: