Answer
$a=3$
Work Step by Step
Substitute $4$ to $x$ in the give equation to obtain:
$4+2a=16+a(4)-6a
\\4+2a=16+4a-6a
\\4+2a=16-2a$
Add $2a$ and subtract $4$ to both sides of the equation to obtain:
$4+2a+2a-4=16-2a+2a-4
\\4a=12$
Divide $4$ on both sides to obtain:
$a=3$
