Edge length = 63 feet
Volume = (length) x (width) x (height)
Volume = (63 ft) x (63 ft) x (63 ft) = (63 ft)³ = 250,047 ft³ .
=====================================
1 yard = 3 ft
63 ft = 21 yards
Volume of the cube = (21 yd) x (21 yd) x (21 yd) = (21 yd)³ = 9,261 yd³
======================================
A slightly different way:
1 yard = 3 ft
1 yard³ = (3 ft)³ = 27 ft³
Volume of the cube = (250,047 ft³) x (1 yd³/27 ft³) = 250,047/27 = 9,261 yd³
