Many math problems are about physics and engineering. In many of these physics problems time is a variable. Time uses the letter "t". Using the basic ideas in algebra can help reduce a math problem to its simplest form making it easier to solve difficult problems. Energy is "e", force is "f", mass is "m", acceleration is "a" and speed of light is sometimes "c". This is used in some famous equations, like f = ma and e=mc^2 (although more complex math beyond algebra was needed to come up with that last equation).