The red superset contains all the Sarcophagi and Mummification cards from Valley of the Kings and Valley of the Kings: Afterlife. Six different cards in the Red set. Both the Sarcophagi and Mummification cards are part of the same set, not two different sets for scoring. Thus getting all 6 different red cards in your tomb scores 6x6=36 points.
See the superset scoring example on page 17 in the rulebook: Combine the Sets by Color Group.