El numero = x
2/3 de x = 1680
2x/3 = 1680
2x = 1680*3
2x = 5040
x = 5040/2
x = 2520
El numero es 2520
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4/9 de x = 1800
4x/9 = 1800
4x = 1800*9
4x = 16200
x = 16200/4
x = 4050
El numero es el 4050