Returns to scale - Constant Function Suppose we have a production function $f(z)=2$.

I am asked to determine whether the function exhibits increasing, decreasing, constant or no returns to scale.

For $t&gt;0$, $f(tz)=2$.

I'm not sure about the answer: should I say the function exhibits no returns to scale whatsoever or take different values for $t$ ($0&lt;t&lt;1 \implies$decreasing returns to scale, $t=1 \implies$ constant returns to scale, $t&gt;1 \implies$ increasing returns to scale)?
You want to find a relation between $tF(z)$ and $F(tz)$ for all $t&gt;1$ (or $0$ for CRS). 

So since $2t=tF(z)&gt;F(tz)=2$ for all $t&gt;1$, we see decreasing returns to scale.