Homework Hint: Problem No. 2/221

This is an easy question (really). Just don't make it too easy.

Suggestion
Start out this question as you would any cable-pulley problem: write down the length of the cable in terms of the two variables of the problem (position of B and the position of A). You should get the following: L = 2*yB + 3*sqrt(y^2+b^2) where yB is the position of block B. Since L is a constant, then dL/dt = 0.

Also see the animation and solution of a similar problem, Problem 2/220. A link to this is provided in the Solution Video links shown to the right.