Hello, rom!
I will assume that a was omitted from the function.
(a) The graph looks like this: Code:

3 + * *
 * : * * : *
 * : * * : *
* : * * : *
 : 18 :
*+*+*+*
 6 12 : 24 30 36
 * : *
 * : *
 * : *
3+ *

(b) The derivative is: .
When metres per hour (rising).
(c) On the graph, we see that the startionary points (horizontal tangents):
. . are at: .
(d) When is
The first time , we have: .
. . Then: .
The next time is
On the graph, we see that for:
. . and it happens again for:
Therefore, the liner can enter the harbour on Monday from 2 pm to 10 pm
. . and on Tuesday from 2 pm to 10 pm.