Density is the ratio of mass to the volume.
The mathematical expression is given as:
[tex]density=\frac{mass}{volume}[/tex]
Now, density of isooctane = [tex]0.692 g/mL[/tex]
Volume = [tex]3.8 gal[/tex]
Since, 1 gallon = 3.78 L
So, 3.8 gal = [tex]3.78 L\times 3.8[/tex]
= [tex]14.364 L[/tex]
As, 1 L = 1000 mL
Therefore, [tex]14.364 L[/tex]= [tex]14.364 L\times 1000 mL[/tex]
Volume in mL = [tex]14364 mL[/tex]
Put the values,
[tex]0.692 g/mL=\frac{mass}{14364 mL}[/tex]
[tex]m = 0.692 g/mL\times 14364 mL[/tex]
= [tex]9939.888 g[/tex]
Hence, mass of 3.8 gal of the gasoline is [tex]9939.888 g[/tex].