To calculate mass from density and volume, use the formula mass = density × volume. In this case, first convert the volume of battery acid from gallons to liters, as density is typically expressed in grams per liter. Next, multiply the density (1.26 g/mL) by the volume in milliliters to find the total mass of the solution. To find the mass of sulfuric acid, multiply the total mass by the percentage of sulfuric acid by mass (38.5%). This method can be applied to similar problems involving density and volume calculations.