A simply support steel beam with a rectangular cross section is loaded as shown. If the beam is replaced with an aluminum beam of the same length and height, what should be the width of the aluminum beam to give the same beam deflection under the same load? $W=6KN,2x=3$ meters, $b=10cm,h=15cm,$ Es $=200$GPa, Ea $=69$GPa.

$34\mathrm{.}4$ cm

$28\mathrm{.}9$

$21\mathrm{.}4$ cm

$3\mathrm{.}5$ cm