Three different positions of the same dice are shown (figure 1 to 3). Find the number on the face opposite to the face having '6'.

5

Step 1)     In a dice there are numbers 1, 2, 3, 4, 5, 6

Step 2)  According to question  5  is common in all the dices and it shares it's boundary with all 1, 2, 3 ,4 except 6.

Step 3)  So, the number 5 is the face opposite the face showing '6'.