consider mixing 40 m^3 of antifreez and 60 m^3 of water.

Mass of resultant mixure = 40 x 800 + 60 x 1000 (considering density of water as 1000k/m^3 .check it)

= 92000

Volume of resultant mixure = 100 - 5 = 95 (since there is decrese of 5% volume)

density = m/v

= 92000/95Answewr