The seven pieces consist of 6 smaller equal pieces and one half cake piece.
Weight of each small piece = 20 g.
So, total weight of the cake = [2 x (20 x6)]g= 240 g.
ANSWER IS 13.
FROM PATTERN 1 WE GET TO KNOW THAT THE PRODUCT OF SQUARE 1 AND 2 SUBTRACTED BY THE THIRD GIVES OUT THE NUMBER IN TRIANGLE.FOR INSTANCE,
5*4-8=12
3*5-4=11
4*5-7=13.