A solid body is in the form of a cube of side A cm at —10°C. When it is heated through a small temperature difference of t°C, its volume increases by B cc. When it is completely converted into liquid at 0°C, its coefficient of volume expansion becomes ‘n’ times that of the substance in solid form. The fractional change in density of the liquid when heated through a temperature difference of  t°C from 0°C is