The idea is to use an international standard - the same units everywhere.
most of the world does SI so more people can understand with it in SI units
most of the world does SI so more people can understand with it in SI units
It's much easier to convert and it is common known (every country uses this except the U.S. since we want to be "different".)
Inches Feet Fluid Ounces Quarts Half-Gallons Gallons Miles Yards
What units? Feet, inches, metres etc?
Linear units, like inches, can't be converted to cubic units. If they could, then you'd be able to calculate your height in gallons.
It depends on the solid, but typically the scientific unit of a solid is grams. SI units are always metric, so that means you would use centimeters or millimeters instead of inches, liters instead of gallons, et cetera.
The answer depends on the units used for the question. Are they 12 inches * 12 inches * 30 inches or are they feet, or metres or miles?
Cubic inches, cubic centimeters, liters, quarts, and gallons
It depends on the units used for 146: microlitres, litres, gallons, whatever.
Square inches is an area, not a volume. You can't convert square inches to gallons. If you meant CUBIC inches, then 682 cu in is 2.95 US Liquid gallons or 2.53 US Dry Gallons.
It depends on the units in which the measures are expressed: inches, feet etc.