There is a very important theorem that can test whether an edge is in MST or not: Source: SO Link
An edge is not in any MST if and only if it is a unique heaviest edge in some cycle
$$\text{Edge not in MST} \Leftrightarrow \text{it is a unique heaviest edge in some cycle} $$
In other words,
$$\text{Edge in MST} \Leftrightarrow \text{it is NOT a unique heaviest edge in some cycle} $$
if $x$ is in MST then it can not be a UNIQUE and HEAVIEST edge in some cycle.
$x$ can not be greater than $110$ which means $x$ is lesser than equal to $110$.
Same goes to $y$ and $z$.
To be in MST, $x, y$, and $z$ can not be the largest weight in the cycle.
i.e.,
- $x \leq 110$
- $y \leq 60$
- $z \leq 80$
Maximum value of $x+y+z=110+60+80=250$.