Moment

The combined centre of mass of the two bricks is at the table edge.
Distance of centre of mass of brick P from table edge = (12 - 4) cm = 8 cm

Ket y be the centre of mass of brick Q from edge of brick P
x - y =12
i.e. y = x - 12

Take moment about combined centre of mass (i.e. edge of table)
W.(8) = W.(4 + y)
where W is the weight of each brick
hence, 8 = 4 + (x - 12)
4 = x - 12
x = 16 cm

The answer is option D

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