let

h1 = 4 ft the height of the first pyramid

b1 = 12 ft^2 the base of the first pyramid

v1 = 16 ft^3 the volume of the first pyramid

h2 = 9 ft the height of the first pyramid

b2 = 36 ft^2 ft^2 the base of the first pyramid

v2 = ? the volume of the second pyramid

since the volume of a pyramid varies jointly as the area of its base and height we can write

v = k*h*b, where k is a constant thus we have

v1 = k*h1*b1 and v2 = k*h2*b2

if we replace the values for v1, h1, b1, h2 and b2 we have

16 = k*4*12

v2 = k*9*36

from the first equation k = 16/(4*12) that is k = 1/3

by replacing k in the second equation

v2 = (1/3)*9*36

v2 = 108 ft^3

the volume of the second pyramid is 108 ft^3.