What volume of water has the same mass as 9.0m3 of ethyl alcohol?

This question requires the knowledge of density. 

The density of ethyl alcohol = 789 kg m⁻³
The density of water = 1000 kg m⁻³

Density = Mass / Volume 

By applying ethyl alcohol,
    789 kg m⁻³ = Mass / 0.9 m³
         Mass     = 710.1 kg
hence the mass of 0.9 m³ ethyl alcohol is 710.1 kg.

Then by applying water,
     1000 kg m⁻³ = 710.1 kg / Volume
      Volume        = 0.7101 m³
                          = 0.7 m³
hence the equal water volume is 0.7 m³

A.(nh4)(2co3)is the correct answer