Answer
$z=12.4$.
Work Step by Step
The given equation is
$\Rightarrow 8.6=z-3.8$
Add $3.8$ to both sides.
$\Rightarrow 8.6+3.8=z-3.8+3.8$
Simplify.
$\Rightarrow 12.4=z$
Check:-
$\Rightarrow 8.6=12.4-3.8$
$\Rightarrow 8.6=8.6$
True.
Hence, the solution is $z=12.4$.
