Question 21264
Like terms are terms, such as: 2x, x, 3x; that are exactly alike. 
ex; 2x and {{{2x^2}}} are not like terms.
Combining them, is just adding or subtracting them, which ever the equation asks.
ex:
3x+4x; they are like terms so you can add them together;
3x+4x=7x
5x-4x; they are like terms so you can subtract them;
5x-4x=x
{{{3x^2}}}+4x; are not like terms, so you CAN NOT add them.
Hope this helps
=)