Here density of the iron d = 7600 kg/m3
volume v = 4cm * 15 cm *20 cm
=1200cm cube
=1.2 *10-3 m3
mass m = ??
According to the formula,
m=d * v
m = 7600 * 1.2 *10-3
mass m = 9.12 kg
Hence,
The mass of the iron block with dimension of 4 cm*15 cm * 20 cm will be 9.12 kg if the density of the iron is 7600 kg/m cube.