Answer
a) 0.072 kg
b) 2.52 cm
Work Step by Step
a) we know that density $\rho = \frac{M}{V}$
where M is the mass and V is the Volume
Volume of the brick $V = L\times b\times\ h$ =$1\ cm\times2\ cm\times 4\ cm = 8\ cm^{3} $
Given density $\rho$ = $9 g/cm^3$
now mass can be calculated by $ m = \rho\times V = 8\ cm^3\times 9\ g/cm^3 = 72\ g = 0.072\ kg$
------------------------------------------
b) cube of this material containing twice the mass of brick, its volume would be twice of the previous one i,e 2V
length is $L = (2V)^{1/3} = (2\times 80\ cm^3)^{1/3} = 2.52\ cm$
