Question 936259
Firstly let us write the data given 

Tallest pyramid
height = h
base = b
h/b = 2/3

b=(3/2) h

Volume of this pyramid= 1/3 * (3/2*h)^2*h
=1/3 * 9/4h^3
=(3/4)h^3

Volume of smaller pyramid

height = h/2
(h/2)/b = 2/3

b= (3h/4)

V= 1/3 * (3h/4)^2*(h/2)

=1/3 * 9h^2/16 *h/2

=3h^3/32

Vol of 3 pyramids = 3*3h^3/32= 9h^3/32

Sum of volumes = 30 million cu.ft

(3h^3/4) +(3h^3/32)= 3*10^7 cu.ft
multiply equation by 32


24h^3+3h^3= 32*3*10^7

27h^3= 96*10^7
h^3= 96/27 *10^7
h=328.82
base = 1.5*328.82=493.24 feet

Smaller pyramid
height = h/2 = 328.82/2=164.4 feet
base = 1.5 * 164.4=246.6 feet

apply formula and find individual volmes