Explanation:
We call like terms only when we have some variables parts. For example 3x and 4x are like terms whereas 3x and 4w are not like terms.
The best thing about line terms are they can be combined together that is added, subtracted, multiplied or divided. For instance
3x+4x=7x or 4x-3x=x.
Lets us learn more by taking example containing more than one variable
3x+2y+4x+7−y
=3x+4x+2y−y+7
=(3+4)x+(2−1)y+7
=7x+y+7
So, 3x+2y+4x+7−y in standard form becomes 7x+y+7