Hi Kayla,
When you are asked to simplify, you combine the terms when they are like.
“like” terms are when variables with their exponents are the same.
examples
5x and 7x are like (as variable are both x and exponent for both is 1)
2x and 3y are not like (as variables x and y are not the same)
4x and 4x^2 are not like (both variables are x, but exponent for the first term is 1, but the exponent for the second term is 2)
check if the terms in the question are like or not, if they are, you can combine them (subtract as in your question)
Please let me know if you have further questions.
Kayla C.
Would you subtract like 7-9 or 9-7?04/10/19