Question 1045713
From the hint that you gave, it should follow that 

{{{200/t - 240/(t+3) = 10}}}.

===> {{{20/t - 24/(t+3) = 1}}}.

<===> {{{-4t+60 = t^2+3t}}}, after simplifying;

<===> {{{t^2 + 7t -60 =(t+12)(t-5) = 0}}}

==> t = 5 hours

===> The speed of the slower ship is {{{240/(t+3) = 240/(5+3) = 240/8 = 30 kph}}}.


ALTERNATE SOLUTION (without initially resorting to t):

Let r = speed of the slower ship.
===> r + 10 = speed of the faster ship

===> {{{240/r - 200/(r+10) = 3}}}

===> r = 30 kph, which gives the speed of the slower ship directly.