Answer:
<em>-1.031 m/s or  </em>
Step-by-step explanation:
We take the length of the rope from the dock to the bow of the boat as y. 
We take x be the horizontal  distance from the dock to the boat.
 We know that the rate of change of the rope length is  = -1 m/s
 = -1 m/s
We need to find the rate of change of the horizontal  distance from the dock to the boat =   = ?
 = ?
for x = 4
Applying Pythagorean Theorem we have
 .... equ 1
    .... equ 1
solving, where x = 4, we have



Differentiating equ 1 implicitly with respect to t, we have

substituting values of 
x = 4
y = 
 = -1
 = -1
into the equation, we get

 = <em>-1.031 m/s</em>
 = <em>-1.031 m/s</em>