What is the answer to puzzle 91 in Professor Layton the lost future?

Puzzle No 91: Strange Glasses, Lost Future.

You need to have solved puzzle 90 first, Enter the big double doors and find three hint coins,

When you get close to the big double doors you will find three more hint coins,

Tap in the doors.

Answer = G is a different shape.

Please see the related link below for a walkthrough of this puzzle