-42=-6(8-3a)+6(1+a)

Solution for -42=-6(8-3a)+6(1+a) equation:

-42=-6(8-3a)+6(1+a)

We simplify the equation to the form, which is simple to understand 
-42=-6(8-3a)+6(1+a)

Reorder the terms in parentheses
-42=+(-48+18a)+6*(1+a)

Remove unnecessary parentheses
-42=-48+18a+6+*(+1+a+)

Reorder the terms in parentheses
-42=-48+18a+(+6+6a)

Remove unnecessary parentheses
-42=-48+18a+6+6a

We move all terms containing a to the left and all other terms to the right. 
-18a-6a=-48+6+42

We simplify left and right side of the equation. 
-24a=0

We divide both sides of the equation by -24 to get a. 
a=-0