How do I open the coffin?

Hint 1 of 14:

Did you examine the painting?

Hint 2 of 14:

The objects in the painting should be familiar.

Hint 3 of 14:

The sceptre, have you found it?

Hint 4 of 14:

It is back in Meldrew Hall.

Hint 5 of 14:

In the umbrella stand in the White Hallway.

Hint 6 of 14:

You can use LAGACH at the writings just south of the tombstone
to get you there and back.

Hint 7 of 14:

The Sceptre fits in the sockets.

Hint 8 of 14:

There are three sockets.

Hint 9 of 14:

Have you learned how to count?