Answer:
BD = 8 cm
Step-by-step explanation:
Point O divides the diagonals proportionally, so ...
... AO/AC = BO/BD = 3/4
Then ...
... BO = BD·3/4 . . . . . multiply by BD
... BD = 4/3·BO = 4/3·(6 cm) . . . . . multiply by 4/3; substitute the value of BO
... BD = 8 cm