solve using energy methods

The assembly consists of two blocks, A and $B,$ each with a

mass of $m_A$ and $m_B,$ respectively. The system is released from

rest in the position shown. The three pulleys in the system are

frictionless and the mass of each can be neglected. A single

cord is wrapped around the entire system and the cord will not

extend. Find the speed of both blocks when block $B$ has

descended a distance $d.$ Use the given values: $m_A=20kg,$

$m_B=30kg$

$d=1\mathrm{.}5m$

Answer: $\{\begin{array}{c}\text{:}[b_B^{}=4\mathrm{.}62\frac{(m)}{(s)}]\\ b_A^{}=1\mathrm{.}54\frac{(m)}{(s)}\end{array}$