Answer:
5475 cubic ft
Explanation:
The volume of a cylinder is given by

where
r = radius of the base
h = height of the cylinder.
Now in our case,
r = 15 / 2 = 7.5 ft
h = 31ft
therefore, the volume is

using π = 3.14 gives

The right-hand side of the above equation simplifies to give

rounding to the nearest whole number gives

Hence, the volume of the grain silo is 5475 cubic ft.