Combine Like Terms (+-)

Simplfify the following expression:  $-8y+9+6$  

Simplfify the following expression:  $6+4r+8r$  

Simplfify the following expression:  $-9+10k-6k$  

Simplfify the following expression:  $4x+4x$  

Simplfify the following expression:  $2z-4z$  

Simplfify the following expression:  $2n+10n$  

Simplfify the following expression:  $-10n+7n$  

Simplfify the following expression:  $5+10n+1+10n$  

Simplfify the following expression:  $a-3+3a-2$  

Simplfify the following expression:  $-7x-10x$