Convert 2.12 gallons to milliliters if 946 mL = 1 qt.?

You need to use two conversion factors, one to get you from gallons to quarts, and the other to get you from quarts to mililiters.

Since 1 gallon is equivalent to 4 quarts (for US units), you'll get

##2.12cancel("gallons") * (4cancel("quarts"))/(1cancel("gallon")) * "946 mL"/(1cancel("quart")) = "1051.5 mL"##

Rounded to three , the number of sig figs given for 2.12 gallons, the answer will be

##"2.12 gallons" = color(green)("1050 mL")##