Pentomino Box Packing : 9×3×3 −21

3 solutions.

1. UXIIIIINN | XXXPPNNNF | UXPPPLLLL
   U.......F | U.......F | U.......L
   VVVZWWTTT | VZZZYWWTF | VZYYYYWTF

2. IIIIIZWWT | XPPZZZYWW | PPPZYYYYW
   X.......T | X.......T | X.......T
   UUVLLLLFT | XUVLNNFFF | UUVVVNNNF

3. IIIIINNNF | XPPLNNFFF | PPPLLLLFT
   X.......T | X.......T | X.......T
   UUVZYYYYW | XUVZZZYWW | UUVVVZWWT