



 
Hi Ralph, In my diagram $r(t)$ is the length of the rope at time $t$ minutes after the man started to pull the rope and $b(t)$ is the distance from the boat to the wharf at the same time. You don't know either $r(t)$ or $b(t)$ but you do know that $r^{\prime}(t) = 2$ meters per minute. Triangle $WSP$ is a right triangle so use Pythagoras' Theorem to write an equation involving $r(t)$ and $b(t).$ Differentiate both sides with respect to $t.$ Penny  


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