AMC 8 1990 Problem 11

The numbers on the faces of this cube are consecutive whole numbers. The sum of the two numbers on each of the three pairs of opposite faces are equal. The sum of the six numbers on this cube is

$\text{(A)}\ 75 \text{(B)}\ 76 \text{(C)}\ 78 \text{(D)}\ 80 \text{(E)}\ 81$