What is 5a - (8 - a) + 4a - 10

5a-8+a+4a-10
5a+a+4a-8-10
10a-18 ** I think

Pretend there is an invisible -1 in front of the parenthesis to distribute, then get rid of the parenthesis, then you can combine like terms.
= 5a - 1(8-a) +4a - 10       
         ^^                      <-- negative (-) times (x) a negative (-) equals positive = (+)
= 5a - 8 + a +4a - 10        
     ^^^               <--Combine like terms      
= 5a +a +4a = 10a
= -8 -10       = -18
= 10a -18

Hope this helps!