First distribute
-8a-2-(a+4)=-51
Then distribute the -
-8a-1-a-4=-51
Then subtract the numbers
-8a-5-a=-51
Combine like terms
-9a-5=-51
Add 5 to both sides
-9a=-46
Divide by -9
a=46/9 write in fraction from
If answer is negative remove by cancel out like terms