Problem: a cube is divided into 64 identical cubelets . each cut is made parallel to some surface of the cube . but before doing that , the cube is painted with green on one set of opposite faces , red on another set of opposite faces , and blue on the third set of opposite faces . how many cubelets are painted with exactly one colour ? 
Options: a ) 12 , b ) 16 , c ) 20 , d ) 24 , e ) 30
d