Subtracting monomials is essentially the same process as adding monomials just as subtraction is the 'addition' of a negative number!
If your child is unfamiliar with the proper identifying terms of a monomial, be sure to cover this before moving on.
Like Terms are monomials with the same VARIABLE part.
N.B. The same variable part emplies the terms have the same variable raised to the same Exponent (power, Index).
Confirm you are adding like terms (identical variables):
Subtract the coefficients:
Keep the variable: a^3b^2c
As you can see, when it comes to subtracting monomials it is simply a case of confirming that the variables are IDENTICAL and simply subtracting the coefficients.
When you are subtracting the coefficients, the rules that apply to those numbers individually remain the same.
Once you are comfortable subtracting monomials, you can move forward and explore how to multiply and divide them also.
We have all of the main topics of elementary math detailed starting at the Basic Math Section or you can explore everything else Printable Math Worksheets has to offer from here.