Question

(Z-6) divided by 3 for z= 15.9

Answer 1

(z-6) turns to (15.9-6) which is 9.9 then divide that by 3 and you get 3.3

Answer 2

Simply plug in $\sf{z=15.9}$ into $\sf{\frac{z-6}{3}}$

So:

$\sf{\frac{15.9-6}{3}}$

Simplify that more:

$\sf{\frac{9.9}{3}}$

And that finally becomes 

$\sf{3.3}$

So when $\sf{z=15.9}$ the answer will be $\boxed{\sf{3.3}}$