like terms would be taking all of the ones with a and getting them alone, all of the ones with b alone, and all plain numbers alone to simplify
1) 2a+3-5a+8b
****= -3a+8b+3****
take 2a-5a and that is your answer
2) 6a+rs-4a+6rs
=2a+rs+6rs
combine the a's 6a-4a
****=2a+7rs****
1rs+6rs combine rs's and that's it :)
**** is the answers