You have to know the formula for the volume of a cone.
In high school, there's no other way.
Volume of a cone = (1 / 3) π (radius)² (height)
Volume = (1 / 3) π (12 inches)² (15 inches)
Volume = 720 π = 2,261.95 cubic inches
Rounded to the nearest cubic inch, that's 2,262 cubic inches.