Answer
$\displaystyle \lim_{t\rightarrow 11}U(t)$ does not exist.
Work Step by Step
In the time before $t=11$, the values of $U(t)$ were $35$, so approaching $t=1$ from the left, we have
$\displaystyle \lim_{t\rightarrow 11^{-}}U(t) =35$
After $t=11$ (to the right of it), we have:
$\displaystyle \lim_{t\rightarrow 1^{+}}U(t) =20.$
We see that the one-sided limits exist, but are not equal.
Thus, $\displaystyle \lim_{t\rightarrow 11}U(t)$ does not exist.
