we add like terms
so remembe that we can add the numbers in front of the placeholders
exg
3a+2a=5a becuase 3+2=5
we cannot add a+b
so
remember the associative property which is a+(b+c)=(a+b)+c
therefor we can move the parenthasees
also remember the commutativer property which is a+b=b+a so we can change
(3a-b)+2a to (3a+2a)-b=(5a)-b=5a-b