The results are as follows:
- At \( t = 0 \), the leak rate is \( 20 \) thousand liters/min.
- At \( t = 60 \), the leak rate is approximately \( 1.8144 \) thousand liters/min.
- The total amount of oil leaked during the first hour is approximately \( 454.6410 \) thousand liters.
Thus, the final answers are:
\[
\boxed{20 \text{ thousand liters/min at } t=0}
\]
\[
\boxed{1.8144 \text{ thousand liters/min at } t=60}
\]
\[
\boxed{454.6410 \text{ thousand liters during the first hour}}
\]