Step 1: Count hidden faces (faces in contact).
Arrange the dice in three columns with heights \(3,2,1\).
Hidden faces come from: bottoms on the floor, vertical contacts in a column, and side contacts between columns.
\[ \begin{aligned} &\text{Bottom faces} = 3,\\ &\text{Vertical contacts in columns } (3\rightarrow2\rightarrow1) = 2+1=3 \text{ contacts } \Rightarrow 2\cdot 3=6 \text{ hidden faces},\\ &\text{Side contacts between columns } (2+1=3 \text{ contacts}) \Rightarrow 2\cdot 3=6 \text{ hidden faces}. \end{aligned} \] Total hidden faces \(= 3+6+6=15\).
Since \(6\) dice have \(6\times 6=36\) faces in all, visible faces \(=36-15=21\) (as stated).
Step 2: Maximization principle.
The sum on all six faces of a die is \(1+2+3+4+5+6=21\).
Hence (for each die) \(\text{visible sum} = 21 - \text{(sum on its hidden faces)}\).
So to maximize the visible total, minimize the sum on hidden faces, putting the smallest possible numbers on the faces in contact, respecting “opposites sum to \(7\)”.
Step 3: Choose the smallest numbers on hidden faces die-by-die.
Label columns left\(\to\)right with heights \(3,2,1\).
Hidden faces per die: \[ \begin{array}{l|c} \text{Die} & \text{Hidden faces (count)} \\ \hline \text{Left column: bottom (A)} & \text{bottom, top (opposites), right }(3) \\ \text{Left column: middle (B)} & \text{bottom, top (opposites), right }(3) \\ \text{Left column: top (C)} & \text{bottom }(1) \\ \text{Middle column: bottom (D)} & \text{bottom/top (opposites), left/right (opposites) }(4) \\ \text{Middle column: top (E)} & \text{bottom, left }(2) \\ \text{Right column: only (F)} & \text{bottom, left }(2) \end{array} \] - For each opposite pair hidden, the minimum sum is \(7\) (unavoidable).
Thus \(A\): \(7+\) one extra face, \(B\): \(7+\) one extra face, \(D\): \(7+7=14\).
- The remaining single hidden faces can take the smallest available numbers \(1,2,\ldots\).
Choose minimally: \[ \begin{aligned} &A:\ 7+1=8,\quad B:\ 7+1=8,\quad C:\ 1,\\ &D:\ 14,\quad E:\ 1+2=3,\quad F:\ 1+2=3. \end{aligned} \] Total minimum on hidden faces \(=8+8+1+14+3+3=37\).
Step 4: Compute the maximum visible sum.
All-face total \(=6\times 21=126\).
Maximum visible \(=126-37=89\).
\[ \boxed{89} \]