Answer
$233\;eV$
Work Step by Step
According to the diagram, an electron in the $n=3$ state has an energy of $E_3=233\;eV$.
Inside the well there is no potential energy $(V)$, and the electron is trapped the well by the "walls" of $450\;eV $potential energy.
Thus, inside the well $V=0$.
Therefore, the kinetic energy $(K)$ of the electron inside the well is
$K=E_3-V$
or, $K=(233-0)\; eV=233\;eV$
