Density of the mixture = mass of the mixture / volume of the mixture
Mass of the mixture = mass of antifreeze solution + mass of water.
Mass of antifreeze solution = density of the antifreeze solution * volume
Mass of antifreeze solution = 0.8g/ml * 5.1 l * 1000 ml / l = 4,080 g
Mass of water = density of water * volume of water = 1.0 g/ml * 3.8 l * 1000 ml / l = 3,800 g
Mass of mixture = 4080 g + 3800 g= 7880 g
Volume of mixture = volume of antifreeze solution + volume of water
Volume of mixture = 5100 ml + 3800 ml = 8900 ml
Density of mixture = 7800 g / 8900 ml = 0.876 g/ml
Specific gravity of the mixture = density of the mixture / density of water = 0.876
Answer: 0.876