Calclus Help

Hi there I am a calclus student and my teacher gave us a take home quiz. I am having trouble with starting it up and I need a bit of help. I don't think I need the answer I just need a jump start a bit of help you know thanks in advance to whoever wishes to help.

Here is the triange not very good looking but I think it gets the job done

Ship B
=       =
=             =
= Y                 =
=                         =
=                      theata  =
Lighthouse rock ===============Ship A
                    X

Ship a is traveling due west toward lighthouse rock at a speed of 15 km per hour. Ship B is traveling due north away from Lighthouse Rock at a speed of 10 km/hr. Let x be the distance between Ship and and lighthouse rock at time t, and let y be the distance between ship B and lighthouse rock at time t.

A.) Find the distance in kilometers, between Ship A and ship B when x =4km and y =3km

This one was easy used a^2+b^2=c^2 got 5 that one was only 1 point out of nine though

B.) Find th rate of change in km/hr of the distance between the two ships when x=4km and y=3km

This one I have no idea I think it might be an optimization problem but I have no idea what two equations to use, I dont even know if it is an optimization problem and I could use your help

C.) Let theta be the angle shown in the figure. Find the rate of change of theta in raidans per hour when x =4km and y =3 km

Once again think its an optimization problem I think I could figure it out if I knew how to do #2 as well

Thanks again for your help once again I don't want just the answer I need a jump start mabybe the answer with the work shown thanks again

Sorry I just realized the triangle does not look very good the hypnose of the triangle is sposed to conect ship b and ship a sorry bout that

express X as a function of time
express Y as a function of time

at all times, the hypotenuse is = sqrt(X^2 + Y^2), which is now a function of time

rate of change = time derivative, by definition

tan(theta) = Y/X, etc

Thank You very much I got 18km/hr for B and .8444 rd/hr I am sure they are both right thank you very much once again I appreacate it.