ok, i think this is the right interpretation for your problem (see the diagram below--ALWAYS DRAW A DIAGRAM WHEN DOING RELATED RATES!)

so obviously there is a right angled triangle here, so the formula we will be using is Pythagoras' formula.

notice that x is increasing at the same rate y is decreasing, so dx/dt = -dy/dt

also notice that when the weight is four feet from the ground, y=4, x = 26 (since its a 30 foot rope, they have to add up to 30) and by pythagoras' formula, z = 25.69

we are told the the car moves 5 feet/s so dz/dt is increasing at 5 ft/s

we are looking for dy/dt when y = 4, here goes:

x^2 = y^2 + z^2

=> 2x dx/dt = 2y dy/dt + 2z dz/dt

=> 2x (-dy/dt) = 2y dy/dt + 2z dz/dt

=> - 2x dy/dt - 2y dy/dt = 2z dz/dt

=> dy/dt (-2x - 2y) = 2z dz/dt

=> dy/dt = [2z dz/dt]/(-2x - 2y)

now plug in all the values

=> dy/dt = [2(25.69)(5)]/(-2(26) - 2(4)) = 256.9/(-52 - 8) = 256.9/(-60)

=> dy/dt = - 4.28 ft/s

note that dy/dt is negative since the length of y according to our diagram is decreasing.

so the rate is just 4.28 ft/s