Hello,
I don't know how you solve this,
this is my resolution:
Let's e = the distance (in miles) between the 2 ships in function of t(time in hour)
[tex]e= \sqrt{(20+24*t)^2+(23*t)^2} =\sqrt{1105t^2+960t+400}\\\\
v=\dfrac{de}{dt} = \frac{2*1105*t+960}{2* \sqrt{1105*t^2+960*t+400}} \\\\
if\ t=15\ then\ v=\dfrac{2*1105*15+960}{2*\sqrt{1105*15^2+960*15+400}} \\\\
=33.22945583.... ( \frac{mi}{h} ) [/tex]
